If the tip was $5.50 and it's 20% of the bill before sales tax, 5.5/x = 2/10 becuase 5.5 divided by the total must be the same as 20%. Cross multiply to find the answer; 5.5 * 10 = 2x, then 55 = 2x, then x = 27.5
You can check by multiplying 27.5 * 0.2 (which is 20%) and that is 5.5 This means that the total cost before tax is $27.50
