The total cost of 7 vests and 7 blouses was $385. Tina bought 9 such vests, 7 such blouses and a cardigan for $471. If the total cost of a dress and a vest was $53, find the difference in cost between the vest and the dress.
Let 1 V be 1 vest.
Let 1 B be 1 blouse.
Let 1 D be 1 dress.

7 V + 7 B = 385 --- (1)

1 V + 1 B = 385 ÷ 7
1 V + 1 B = 55 --- (2)

1 V + 1 D = 53 --- (3)

9 V + 7 B + 1 D = 471 --- (4)

(4) - (1)
(9 V + 7 B + 1 D) - (7 V + 7 B) = 471 - 385 
9 V - 7 V + 7 B - 7 B + 1 D = 86

2 V + 1 D = 86 --- (5)

(5) - (3)
(2 V + 1 D) - (1 V + 1 D) = 86 - 53
2 V - 1 V + 1 D - 1 D = 33
2 V - 1 V = 33

1 V = 33

From (3)
1 V + 1 D = 53
33 + 1 D = 53

1 D = 53 - 33 = 20

Difference in the cost between the vest and the dress
= 1 V - 1 D
= 33 - 20
= $13

Answer(s): $13