4 pairs of pants for $18.
Divide price by quantity to get the cost of 1 pair of pants:
18 / 4 = 4.50 per pair.
Divide 27 by 4.50 to find number of pairs:
27 / 4.5 = 6
6 pairs of pants can be cleaned for $27.
Using PEMDAS
(Parenthesis)(Exponents)(Multiplication/Division)(Addition/Subtration)
So:


X + 8x = 81
9x = 81, x = 9
y = 8(9), y = 72
Solution: (9, 72)