How do I manipulate a formula and create and number equation out of some give information?

Question

Ex. The cost of the meal plus a 15% tip was $24.15. 

I need this changed to a number equation. 

Answer 1

cost of meal = x

 

tip= x"*15%=x*0.15=0.15x

 

x+0.15x = 24.15     number equation

 

to find the cost of meal solve this equation