If Adam buys 3 marbles and 4 stickers, it costs $47.80.
If Adam buys 4 marbles and 3 stickers, he will have $60 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)
3 marbles + 4 stickers = 47.80 --- (1)
4 marbles + 3 stickers = 47.80 - 60 = 41.80 --- (2)

(1) + (2)
7 marbles + 7 stickers = 89.60 --- (3)

(3) _{÷ 7}
1 marble + 1 sticker = 89.60 ÷ 7 = 12.80 --- (4)

Cost of 1 marble and 1 sticker = $12.80

(b)
(4) _{x 3}
3 marbles + 3 stickers = 3 x 12.80 = 38.40 --- (5)

(2) - (5)
4 marbles + 3 stickers - 3 marbles - 3 stickers = 41.80 - 38.40
4 marbles - 3 marbles - 3 stickers + 3 stickers = 3.40
1 marble = 3.40

Cost of 1 marble = $3.40

(c)
Substitute 1 marble = 3.40 into (4).

1 marble + 1 sticker = 12.80
3.40 + 1 sticker = 12.80
1 sticker = 12.80 - 3.40 = 9.40

Cost of 1 sticker = $9.40

Answer(s): (a) $12.80; (b) $3.40; (c) $9.40