Bobby buys a blazer, a windbreaker and a skirt. The average cost of these items is $36. The cost of the skirt is four times the total cost of the blazer and the windbreaker. If the blazer costs $15, find the difference in cost between the windbreaker and the skirt.
Total cost of the 3 items
= 3 x 36
= $108

Total cost of the blazer and the windbreaker = 1 u
Cost of the skirt = 4 u

Total cost of the 3 items 
= 1 u + 4 u
= 5 u

5 u = 108 

1 u = 108 ÷ 5 = 21.60

Total cost of the blazer and the windbreaker = $21.60

Cost of the windbreaker 
= 21.60 - 15
= $6.60

Cost of the skirt
= 4 u
= 4 x 21.60
= $86.40

Difference in cost between the windbreaker and the skirt
= 86.40 - 6.60
= $79.80

Answer(s): $79.80