Question 836211
You are right! There is no way to tell the tax rate from the info given. 

We also don't know if the tip is on the meal plus tax or just on the meal.
Very poorly written question.
100.725 if we and 18.5% to the 85 dollars.
The cost of the meal itself  will remain unknown but meal, tax and tip was $100.73 
I would have left $100 and be done with it. 18.5 % is too much of a tip anyways