The cost of producing oil is partly constant and partly varies as the number of bottles produced. The total cost of producing 8 bottles is R500, and of producing 20 bottles is R1160. Find the total cost of producing 40 bottles.
cost = mb + c
given: when b = 8 , cost = 500
500 = 8m + c **
given: when b = 20, cost = 1160
1160 = 11m + c ***
subtract ** from ***
660 = 3m
m = 220
go back to ** to find c
now you have the cost equation, sub in b = 40 to find the cost