The value of expression (10y-20) depends on the value of y. Verify this by giving five different values of y and finding for each y the value of (10y-20). From the different values of (10y-20) you obtain. Do you see a solution to 10 y-20 = 50? If there is no solution, try giving more values to y and find whether the condition 10y - 20 = 50 is met.