

Explanation
Let C be the cost and n the number of tourists. then C = x + ny. Where x and y are constants
740 = x + 20y...........(1)
960 = x + 30y.............(2)
Solving (1) and (2) simultaneously will yield x = 300 and y = 22.
Then, C = 300 + 22n.
If we substitute 15 for n this implies that C = 300 + (22 x 15)= $630.00

