Answer
a. P(x) = 20x - 10000
b. $390000
Work Step by Step
a. Profit is revenue - cost
P(x) = R(x) - C(x)
Substitute R(x) = 50x and C(x) = 10000 + 30x into P(x) = R(x) - C(x)
P(x) = 50x - (10000 + 30x)
P(x) = 20x - 10000
b. P(20000) = 20(20000) - 10000
P(20000) = 390000