Trying to figure out Riemann sum? Any ideas? What the answer is?

Bus Econ 4.2.19 Question Help A record club has found that the marginal profit, P'(x), in cents, is given by P'(x) = - 0.0005x* +0.23x"+ 55.5x for x $ 500, where x is the number of members currently enrolled in the club. Approximate the total profit when 300 28,000-JP'(x)= = 0.0005x3 +0.23x2 + 55.5x members are enrolled by computing the sum _ P' (x; ) Ax with Ax =50. 22,400- Q Marginal prof 16,800 11,200 5,600 100 200 300 400 500 Number of members The total profit when 300 members are enrolled is approximately $1