Ivory bought 9 textbooks of the same kind during the Grand Opening Sale. Xuan bought 3 of the same textbooks. Xuan also bought 3 stickers at $2.70 each. Altogether, she spent $2.70 more than Ivory. What was the amount Xuan spent?
Amount that Xuan spent on 3 stickers
= 3 x 2.70
= $8.10

Let the cost of each textbook be 1 u. 

Amount that Ivory spent = 9 u

Amount that Xuan spent =  3 u + 8.10

Xuan spent $2.70 more than Ivory.  If Ivory spent another $2.70, she would spend the same amount as Xuan.

9 u + 2.70 = 3 u + 8.10
9 u - 3 u = 8.10 - 2.70
6 u = 5.40

1 u = 5.40 ÷ 6 = 0.90

Cost of each textbook
= 1 u
= $0.90

Amount that Xuan spent
= 3 x 0.90 + 8.10
= 2.70 + 8.10
= $10.80

Answer(s): $10.80