If Adam buys 5 marbles and 6 stickers, it costs $70.80.
If Adam buys 6 marbles and 5 stickers, he will have $1.90 left.

1. Find the cost of 1 marble and 1 sticker.
2. Find the cost of 1 marble.
3. Find the cost of 1 sticker.

(a)
5 marbles + 6 stickers = 70.80 --- (1)
6 marbles + 5 stickers = 70.80 - 1.90 = 68.90 --- (2)

(1) + (2)
11 marbles + 11 stickers = 139.70 --- (3)

(3) _{÷ 11}
1 marble + 1 sticker = 139.70 ÷ 11 = 12.70 --- (4)

Cost of 1 marble and 1 sticker = $12.70

(b)
(4) _{x 5}
5 marbles + 5 stickers = 5 x 12.70 = 63.50 --- (5)

(2) - (5)
6 marbles + 5 stickers - 5 marbles - 5 stickers = 68.90 - 63.50
6 marbles - 5 marbles - 5 stickers + 5 stickers = 5.40
1 marble = 5.40

Cost of 1 marble = $5.40

(c)
Substitute 1 marble = 5.40 into (4).

1 marble + 1 sticker = 12.70
5.40 + 1 sticker = 12.70
1 sticker = 12.70 - 5.40 = 7.30

Cost of 1 sticker = $7.30

Answer(s): (a) $12.70; (b) $5.40; (c) $7.30