a. Fiona's total bill before the tip was approximately $72.50.
b. Fiona received $4.45 in change after paying the bill and the tip.
How to find Fiona's total bill before the tip
(a) To find Fiona's total bill before the tip, set up the equation:
Tip amount = Total bill * Tip percentage
Given that the tip amount is $13.05 and the tip percentage is 18%, we have:
$13.05 = Total bill * 0.18
To solve for the total bill, divide both sides of the equation by 0.18:
Total bill = $13.05 / 0.18 ≈ $72.50
Therefore, Fiona's total bill before the tip was approximately $72.50.
(b) To find out how much change Fiona received after paying the bill and the tip, subtract the total bill and the tip from the cash she had:
Change = Cash - (Total bill + Tip amount)
Given that Fiona had $90 in cash and we found that the total bill was $72.50 and the tip was $13.05, we have:
Change = $90 - ($72.50 + $13.05)
= $90 - $85.55
= $4.45
Therefore, Fiona received $4.45 in change after paying the bill and the tip.