To answer this question you can set up an equation that represents the total amount of the bill plus the tip.
115%x = $31.05 (where x is the amount before the tip)
1.15x = 31.05; divide both sides
by 1.15
x =$27
$31.05 - $27 = $4.05
The price of the meal was $27, and the tip was $4.05 .
