Shelley earned 20% more money in tips waitressing this week than last week. This week she earned $72.00 in tips waitressing. How much money did Shelley earn last week in tips?

To determine the Earnings of Shelley last week, we need to make relations with the values that are given. We let x as the total amount she earned last week by x and y as the additional amount she earned this week We do as follows:

20% additional amount she earned this week = y / 72 - y

y = $ 12

x = 72 - 12 = $60 total earnings last week