Problem: -4(6-y)+4=-4
step 1: -24-4y+4=-4
step 2: -20-4y=-4
step 3: -4y=16
step 4: y=-4

what step was the mistake made?
what is the correct solution?

Suppose that the price p, in dollars, and the number of sales, x, of a certain item follow the equation 4 p plus 4 x plus 2 pxequals56. suppose also that p and x are both functions of time, measured in days. find the rate at which x is changing when xequals2, pequals6, and startfraction dp over dt endfraction equals1.5.