Answer: $15.21
Step-by-step explanation:
Given
Joe's lunch cost $13.00 without tax
He tipped the waiter with 17% of bill without tax
So, the amount of tip is

Total amount that food costs without tax is

Don’t know if there’s much of an equation for it, but I guess the best way to write it out is 10 + x = -18. Then, you would subtract the 10 from both sides in order to isolate the x. So then you’re left with x = -28. So -28 is your answer.
There is no difficulty in this problem until you construct the figures. How can we do it is shown in the attached picture. After drawing PRST, from the point P, we can draw PMKD and later we can complete PMCT as a result. From this picture, we can see that the side of PMCT is also a. Then, the area of this square is
20% of 89.75 is 17.95

so :

the Trina's coupon will subtract the answer by 10%:
10%of 71.8 is 7.18

so the final answer is:

she has to pay $64.62
hope this helps
If You mean A sum to write here's one :
31+3