Solve the Problem $\$ 400$ Per Person Plus $\$ 3$ Per Person for Each Unsold Seat on the Plane

Solve the problem.
-A charter flight charges a fare of $\$ 400$ per person plus $\$ 3$ per person for each unsold seat on the plane. If the plane holds 213 passengers and if $x$ represents the number of unsold seats, find an expression for the total revenue received for the flight. (Hint: multiply the number of seats sold, 213 - $x$ , by the price per ticket) .

A) $R(x) =x(213-x)$
B) $R(x) =(213-x) (400+3)$
C) $R(x) =(213-x) (400+3 x)$
D) $R(x) =x(400+3 x)$