Item 12 seven out of every 8 students surveyed owns a bike. the difference between the number of students who own a bike and those who do not is 72. how many students were surveyed?

                                       so for this equation, I would do 7/8 = 72/x
1     72
-  =   -               
8     x

Cross multiply to get 72 * 8 = 1x
solve for X                   576 = x