Help with a Java Program!

I am a beginner of Java programing, i came across this problem and am unable to solve this. Please Help!!

This is the Problem..

For a scholarship organization: Scholarship can be allotted to only one student per family. There is a collection of 20 Student objects (class given below).
You are supposed to write a method to return List with distinct last names. E.g If Students are John Doe, John Lincoln, Amy Doe, Foo Bar => then output should return Student objects for John Doe, John Lincoln, Foo Bar. You are allowed to change the Student Class.
Method signature should be List findStudentsWithDistinctLastNames( List allStudents )
Also write another method that finds out how many students applied from each family (i.e. same last name). The output of this method can be a Map.

public class Student {

private String firstName;

private String lastName;

public String getFirstName() {
return firstName;
}

public void setFirstName( String firstName ) {
this.firstName = firstName;
}

public String getLastName() {
return lastName;
}

public void setLastName( String lastName ) {
this.lastName = lastName;
}
}