If Adam buys 4 stickers and 5 marbles, it costs $53.40.
If Adam buys 5 stickers and 4 marbles, he will need another $0.30.

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

(a)
4 stickers + 5 marbles = 53.40 --- (1)
5 stickers + 4 marbles = 53.40 + 0.30 = 53.70 --- (2)

(1) + (2)
9 stickers + 9 marbles = 107.10 --- (3)

(3) _{÷ 9}
1 sticker + 1 marble = 107.10 ÷ 9 = 11.90 --- (4)

Cost of 1 sticker and 1 marble = $11.90

(b)
5 stickers + 4 marbles = 53.70 --- (2)

(4) _{x 4}
4 stickers + 4 marbles = 4 x 11.90 = 47.60 --- (5)

(2) - (5)
5 stickers + 4 marbles - 4 stickers - 4 marbles = 53.70 - 47.60
5 stickers - 4 stickers + 4 marbles - 4 marbles = 6.10
1 sticker = 6.10

Cost of 1 sticker = $6.10

(c)
Substitute 1 sticker = 6.10 into (4).

1 sticker + 1 marble = 11.90
6.10 + 1 marble = 11.90
1 marble = 11.90 - 6.10 = 5.80

Cost of 1 marble = $5.80

Answer(s): (a) $11.90; (b) $6.10; (c) $5.80