Carol goes on vacation to Washington, D.C., where the sales tax on meals is 10%.

Carol goes on vacation to Washington, D.C., where the sales tax on meals is 10%. She goes to a restaurant for dinner. Carol leaves a 15% tip on the price of her meal before the sales tax is added, and the tax is calculated on the pre-tip amount. She spends a total of $27.50 for dinner. What is the cost of her dinner without tax or tip? Write an equation to represent this situation.