Answer:
C = 0.75 x number of hotdogs sold
Because the cost you earn depends on the number of hotdogs you sell for the cost. Also, 75 cents in written as 0.75, because you sill be expecting to get the overall money in Dollars. You can just write it as 75 if you want, though
R = C - 450
Revenue will be the amount you get after selling the hotdogs and paying off everything else. In other words, the profit. So, revenue equals the amount you paid for start-ups subtracted from the money you earnt now
Hope this helps