java program that uses abstract class,abstract methods and polymorphism to do calculations..?i need an idea of what i should be doing

Look in your text book, there should be enough examples there to get you started.

You should be writing an abstract class that declares abstract methods, then a class that extends that abstract class and implements those abstract methods, then a third class that uses that extended class (probably in a variable declared as the abstract class type) that uses those implemented methods to perform some calculations.

nah, he should get himself a time machine so he can go back in time to where he has enough time to do his homework that it's no longer "urgent".