Teacher Xiao Wu went to the sporting goods store and bought 30 different balls, red and white, and went back to school as the sports team leader.

According to the meaning of the question, each red ball is 45÷3= 15 (yuan) more expensive than the white ball, so the price of the white ball is 55- 15=40 (yuan). Suppose you buy x white balls and y red balls, X+Y = 30 ① 40x+55Y = 655.