Answer:
X - X * 0.15 = 0.85X
X * 0.85 = X - X * 0.15
Both of these expressions can be used to find the price of any lawnmower pre-tax this weekend. The first expression calculates the price by subtracting 15% of the original price from the original price, and the second expression calculates the price by multiplying the original price by 85%.