The total cost of 9 jumpsuits and 9 vests was $603. Tina bought 11 such jumpsuits, 9 such vests and a cardigan for $712. If the total cost of a sweater and a jumpsuit was $69, find the difference in cost between the jumpsuit and the sweater.
Let 1 J be 1 jumpsuit.
Let 1 V be 1 vest.
Let 1 S be 1 sweater.

9 J + 9 V = 603 --- (1)

1 J + 1 V = 603 ÷ 9
1 J + 1 V = 67 --- (2)

1 J + 1 S = 69 --- (3)

11 J + 9 V + 1 S = 712 --- (4)

(4) - (1)
(11 J + 9 V + 1 S) - (9 J + 9 V) = 712 - 603 
11 J - 9 J + 9 V - 9 V + 1 S = 109

2 J + 1 S = 109 --- (5)

(5) - (3)
(2 J + 1 S) - (1 J + 1 S) = 109 - 69
2 J - 1 J + 1 S - 1 S = 40
2 J - 1 J = 40

1 J = 40

From (3)
1 J + 1 S = 69
40 + 1 S = 69

1 S = 69 - 40 = 29

Difference in the cost between the jumpsuit and the sweater
= 1 J - 1 S
= 40 - 29
= $11

Answer(s): $11