Almost done. Have doubts, many.

interfaces-1.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module org.jetbrains.idea.maven.project.MavenProjectsManager.isMavenModule="true" type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" LANGUAGE_LEVEL="JDK_1_5">
+    <output url="file://$MODULE_DIR$/target/classes" />
+    <output-test url="file://$MODULE_DIR$/target/test-classes" />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src/main/java" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/java" isTestSource="true" />
+      <excludeFolder url="file://$MODULE_DIR$/target" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" scope="TEST" name="Maven: junit:junit:4.12" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.hamcrest:hamcrest-core:1.3" level="project" />
+  </component>
+</module>

src/main/java/io/zipcoder/interfaces/Educator.java

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+package io.zipcoder.interfaces;
+
+public enum Educator implements Teacher {
+    Leon(1l, "Hunter"), Dolio(2l, "Durant"), Kris(3l, "Younger");
+    String name;
+    Long id;
+    Double timeWorked;
+
+    Educator(Long id, String name) {
+        this.id = id;
+        this.name = name;
+    }
+
+    public void teach(Learner learner, double numberOfHours) {
+        learner.learn(numberOfHours);
+        this.timeWorked += numberOfHours;
+    }
+
+    public void lecture(Learner[] learners, double numberOfHours) {
+        double numberOfHoursPerLearner = numberOfHours / learners.length;
+        for (Learner element : learners) {
+            element.learn(numberOfHoursPerLearner);
+        }
+        this.timeWorked += numberOfHours;
+    }
+}

src/main/java/io/zipcoder/interfaces/Instructor.java

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+package io.zipcoder.interfaces;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+public class Instructor extends Person  implements Teacher{
+    public Instructor(Long id, String name) {
+        super(id, name);
+    }
+
+    public void teach(Learner learner, double numberOfHours) {
+learner.learn(numberOfHours);
+    }
+
+    public void lecture(Learner[] learners, double numberOfHours) {
+        double numberOfHoursPerLearner = numberOfHours / learners.length;
+        for(Learner element:learners){
+            element.learn(numberOfHoursPerLearner);
+        }
+    }
+}

src/main/java/io/zipcoder/interfaces/Instructors.java

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+package io.zipcoder.interfaces;
+
+public class Instructors extends People<Instructor>{
+
+
+
+    static final Instructors INSTANCE= new Instructors();
+
+    public Instructors(){
+    this.add(new Instructor(1l,"Leon Hunter"));
+    this.add(new Instructor(2l,"Dolio Durant"));
+    this.add(new Instructor(3l,"Kris Younger"));
+    }
+
+    public static Instructors getINSTANCE() {
+        return INSTANCE;
+    }
+}

src/main/java/io/zipcoder/interfaces/Learner.java

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+package io.zipcoder.interfaces;
+
+public interface Learner {
+    public void learn(double numberOfHours);
+    public Double getTotalStudyTime();
+}