Total revenue R(q) = ∫R'(q) dq = ∫(240 - 18√q)dq = 240q - 12q^3/2
R(100) = 240(100) - 12(100)^3/2 = 24000 - 12(1000) = $12,000
Marginal revenue at 100 units R'(100) = 240 - 18√100 = 240 - 18(10) = $60
Revenue at 101 units = R(101) = 240(101) - 12(101)^3/2 = 24,240 - 12,180 = $12,060