Shiyun buys a sweater, a dress, a blazer and a vest. The average cost of these items is $45. The total cost of the blazer and the vest is ⁴₅ of the total cost of the sweater and the dress. If the sweater costs $14.90 and the vest costs $9.20, find the difference in cost between the dress and the blazer.
Total cost of the 4 items
= 4 x 45
= $180

Total cost of the blazer and the vest = 4 u
Total cost of the sweater and the dress = 5 u

Total cost of the 4 items
= 4 u + 5 u
= 9 u

9 u = 180

1 u = 180 ÷ 9 = 20

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

Cost of the blazer
= 80 - 9.20
= $70.80

Total cost of the sweater and the dress
= 5 u
= 5 x 20
= $100

Cost of the dress
= 100 - 14.90
= $85.10

Difference in cost between the dress and the blazer
= 85.10 - 70.80
= $14.30

Answer(s): $14.30