If Adam buys 4 marbles and 5 stickers, it costs $49.90.
If Adam buys 5 marbles and 4 stickers, he will have $2.60 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)
4 marbles + 5 stickers = 49.90 --- (1)
5 marbles + 4 stickers = 49.90 - 2.60 = 47.30 --- (2)

(1) + (2)
9 marbles + 9 stickers = 97.20 --- (3)

(3) _{÷ 9}
1 marble + 1 sticker = 97.20 ÷ 9 = 10.80 --- (4)

Cost of 1 marble and 1 sticker = $10.80

(b)
(4) _{x 4}
4 marbles + 4 stickers = 4 x 10.80 = 43.20 --- (5)

(2) - (5)
5 marbles + 4 stickers - 4 marbles - 4 stickers = 47.30 - 43.20
5 marbles - 4 marbles - 4 stickers + 4 stickers = 4.10
1 marble = 4.10

Cost of 1 marble = $4.10

(c)
Substitute 1 marble = 4.10 into (4).

1 marble + 1 sticker = 10.80
4.10 + 1 sticker = 10.80
1 sticker = 10.80 - 4.10 = 6.70

Cost of 1 sticker = $6.70

Answer(s): (a) $10.80; (b) $4.10; (c) $6.70