Gillian bought 9 textbooks of the same kind during the Valentine's Day Sale. Julie bought 4 of the same textbooks. Julie also bought 3 erasers at $2.70 each. Altogether, she spent $1.10 more than Gillian. What was the amount Julie spent?
Amount that Julie spent on 3 erasers
= 3 x 2.70
= $8.10

Let the cost of each textbook be 1 u. 

Amount that Gillian spent = 9 u

Amount that Julie spent =  4 u + 8.10

Julie spent $1.10 more than Gillian.  If Gillian spent another $1.10, she would spend the same amount as Julie.

9 u + 1.10 = 4 u + 8.10
9 u - 4 u = 8.10 - 1.10
5 u = 7.00

1 u = 7.00 ÷ 5 = 1.40

Cost of each textbook
= 1 u
= $1.40

Amount that Julie spent
= 4 x 1.40 + 8.10
= 5.60 + 8.10
= $13.70

Answer(s): $13.70