Answer: the most expensive painting is $10000
Explanation:
Let x represent the amount for which the first painting was sold. One painting is sold for 5 times the amount of a second. This means that
x = 5y
The third was sold for $1500. If the total sale was for $13500, it means that
5y + y + 1500 = 13500
6y + 1500 = 13500
6y = 13500 - 1500 = 12000
y = 12000/6 = 2000
x = 5y = 5× 2000 = 10000