Shiyun buys a blazer, a jumpsuit, a vest and a skirt. The average cost of these items is $36. The total cost of the vest and the skirt is ⁴₅ of the total cost of the blazer and the jumpsuit. If the blazer costs $10.90 and the skirt costs $8.30, find the difference in cost between the jumpsuit and the vest.
Total cost of the 4 items
= 4 x 36
= $144

Total cost of the vest and the skirt = 4 u
Total cost of the blazer and the jumpsuit = 5 u

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

9 u = 144

1 u = 144 ÷ 9 = 16

Total cost of the vest and the skirt
= 4 u
= 4 x 16
= $64

Cost of the vest
= 64 - 8.30
= $55.70

Total cost of the blazer and the jumpsuit
= 5 u
= 5 x 16
= $80

Cost of the jumpsuit
= 80 - 10.90
= $69.10

Difference in cost between the jumpsuit and the vest
= 69.10 - 55.70
= $13.40

Answer(s): $13.40