a)
p(x) = 5000 - 5000/100·x = 5000 - 50·x
E(x) = p(x)·x = (5000 - 50·x)·x = 5000·x - 50·x^2
b)
m = Δy/Δx = (116000 - 80000)/(80 - 20) = 600
K(x) = m·(x - Px) + Py = 600·(x - 20) + 80000 = 600·x + 68000
c)
G(x) = E(x) - K(x) = (5000·x - 50·x^2) - (600·x + 68000) = - 50·x^2 + 4400·x - 68000
d)~plot~ 5000 - 50*x;5000*x - 50*x^2;600*x + 68000;- 50*x^2 + 4400*x - 68000;[[-10|110|-20000|150000]] ~plot~