Consider that company increases the annual subscription by x So, x subscribe will discontinuous the service. /. Total revenue of company after that increment is given by R(x) = (500 - x)(300 + x) -R'(x) = -2x + 200 = R'' (x) = 0 2x = 200 = x = 100 Also R'' (x) = -2 < 0 So, R(x) is maximum when x = 100