Well you have to find the common denominator. You have to look for the common multiples. When you find it (12) you have to multuply the numerator the same you multipied the denominator. So it's 8/12-3/12. 8-3=5 and the denominstor stays the same.
Hurry and do it before the marking period ends. You could really use good grades to get in a good college so you should get some sleep then drink some water and try and do your work.