Answer:
Let "b" be the total bill before the tip.
The tip was 18% of the bill, or 0.18 * b.
The tip was also $4.50, so we can set up the equation 0.18b = $4.50.
Solving for b, we get:
0.18b = $4.50
b = $4.50 / 0.18
b = $25
Therefore, Sierra's total bill before the tip was $25.