We assume, that the number 25 is 100% - because it's the output value of the task.
25/x=100/28
(25/x)*x =(100/28)*x - we multiply both sides of the equation by x
25 = 3.57142857143*x - we divide both sides of the equation by (3.57142857143) to get x
25/3.57142857143 = x
x=7
