Irene buys a shirt, a skirt, a windbreaker and a vest. The average cost of these items is $21. The total cost of the windbreaker and the vest is ²₅ of the total cost of the shirt and the skirt. If the shirt costs $11.50 and the vest costs $12.10, find the difference in cost between the skirt and the windbreaker.
Total cost of the 4 items
= 4 x 21
= $84

Total cost of the windbreaker and the vest = 2 u
Total cost of the shirt and the skirt = 5 u

Total cost of the 4 items
= 2 u + 5 u
= 7 u

7 u = 84

1 u = 84 ÷ 7 = 12

Total cost of the windbreaker and the vest
= 2 u
= 2 x 12
= $24

Cost of the windbreaker
= 24 - 12.10
= $11.90

Total cost of the shirt and the skirt
= 5 u
= 5 x 12
= $60

Cost of the skirt
= 60 - 11.50
= $48.50

Difference in cost between the skirt and the windbreaker
= 48.50 - 11.90
= $36.60

Answer(s): $36.60