5 stickers and 1 marble cost $22.90.
1 sticker and 5 marbles cost $11.30.

1. Find the cost of 1 sticker and 1 marble.
2. Find the cost of 1 marble.
3. Find the cost of 1 sticker.
4. Find the cost of 9 stickers and 9 marbles.

(a)
5 stickers + 1 marble = 22.90 --- (1)
1 sticker + 5 marbles = 11.30 --- (2)

(1) + (2)
6 stickers + 6 marbles = 22.90 + 11.30
6 stickers + 6 marbles = 34.20 --- (3)

(3) _{÷ 6}
6 stickers + 6 marbles = 34.20
1 sticker + 1 marble = 34.20 ÷ 6
1 sticker + 1 marble = 5.70 --- (4)

(b)
(2) - (4)
(1 sticker + 5 marbles) - (1 sticker + 1 marble) = 11.30 - 5.70
1 sticker - 1 sticker + 5 marbles - 1 marble = 5.60
4 marbles = 5.60
1 marble = 5.60 ÷ 4 = 1.40

Cost of 1 marble = $1.40

(c)
Substitute 1 marble = 1.40 into (4).
1 sticker + 1 marble = 5.70
1 sticker + 1.40 = 5.70
1 sticker = 5.70 - 1.40 = 4.30

Cost of 1 sticker = $4.30

(d)
(4) _{x 9}
1 sticker + 1 marble = 5.70
9 x (1 sticker + 1 marble) = 9 x 5.70
9 stickers + 9 marbles = 51.30

Cost of 9 stickers and 9 marbles = $51.30

Answer(s): (a) $5.70; (b) $1.40; (c) $4.30; (d) $51.30