Gwen buys a blazer, a dress, a vest and a shirt. The average cost of these items is $35. The total cost of the vest and the shirt is ³₄ of the total cost of the blazer and the dress. If the blazer costs $15.40 and the shirt costs $10.10, find the difference in cost between the dress and the vest.
Total cost of the 4 items
= 4 x 35
= $140

Total cost of the vest and the shirt = 3 u
Total cost of the blazer and the dress = 4 u

Total cost of the 4 items
= 3 u + 4 u
= 7 u

7 u = 140

1 u = 140 ÷ 7 = 20

Total cost of the vest and the shirt
= 3 u
= 3 x 20
= $60

Cost of the vest
= 60 - 10.10
= $49.90

Total cost of the blazer and the dress
= 4 u
= 4 x 20
= $80

Cost of the dress
= 80 - 15.40
= $64.60

Difference in cost between the dress and the vest
= 64.60 - 49.90
= $14.70

Answer(s): $14.70