Answer: the price of Zoe's dinner before sales tax and tip was $60
Explanation:
Let x represent the original price of the dinner. If the sales tax rate of the dinner is 11%, it means that the amount of tax that Zoe paid would be
11/100 × x = 0.11 × x = 0.11x
She also gave a tip of 20%. Assuming she gave the tip on the original price of the dinner, then the amount of tip that she gave would be
20/100 × x = 0.2 × x = $0.2x
If Zoe paid 18.60 in sale taxes and tip on her dinner, it means that
0.2x + 0.11x = 18.60
0.31x = 18.6
x = 18.6/0.31
x = $60