Question

A number subtracted from 90 is three times that number

Answer 1

90 - x = 3xnow you need to solve for x 
By combining the x-terms, we get 90 = 4x. Dividing both sides of the equation by 4, we get x = 2.25, or 9/4. 

Answer 2

90-n=3n
90=4n
22.5=n

Final answer 22.5