K(x) = 22·x + C
p(x) = - 1/8000·(x - 60000) + 45 = 52.5 - 0.000125·x
E(x) = p(x)·x = 52.5·x - 0.000125·x^2
G(x) = E(x) - K(x) = (52.5·x - 0.000125·x^2) - (22·x + C) = - 0.000125·x^2 + 30.5·x - C
G'(x) = 30.5 - 0.00025·x = 0 --> x = 122000
p(122000) = 52.5 - 0.000125·122000 = 37.25 €