x = - 0.25·p + 920
p = 3680 - 4·x
G(x) = x·(3680 - 4·x) - (0.0457·x^3 - 2.8536·x^2 + 312·x + 7900)
G(x) = - 0.0457·x^3 - 1.1464·x^2 + 3368·x - 7900
G'(x) = - 0.1371·x^2 - 2.2928·x + 3368 = 0 --> x = 148.6 ME
G(148.6) = - 0.0457·148.6^3 - 1.1464·148.6^2 + 3368·148.6 - 7900 = 317311 GE