Get 3 Xs in a row vertical or horizontal or diagonal. To get your X where you want it, you need to answer an addition, subtraction, multiplication or division problem. If you're right, you have your X. If not, the computer blocks you with an O. Authors: Upuli Amarasinghe, Corey Hamby, Alfred Johnson II and Arthur Marques. Final testing, debugging and publishing by Upuli Amarasinghe, Corey Hamby, Tim Thomasma and Byron Wall.