Write a program that teaches arithmetic to a young child. The program tests addition and subtraction. In Level 1, it tests only addition of whole numbers less than ten whose sum is less than ten. In level 2, it tests addition of arbitrary single digit whole numbers. In level 3, it tests subtraction of single digit whole numbers with a non-negative difference.

Generate random problems and get the players' input. The player gets up to two tries per problem. Advance from one level to the next when the player has achieved a score of five correct answers.

Make classes for the test and for each level. Make a superclass Level for the classes Level1, Level2, and Level3 so that the method checkAnswer() need only be written once in Leveland will be inherited.