4 stickers and 1 marble cost $11.10.
1 sticker and 4 marbles cost $8.40.

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 8 stickers and 8 marbles.

(a)
4 stickers + 1 marble = 11.10 --- (1)
1 sticker + 4 marbles = 8.40 --- (2)

(1) + (2)
5 stickers + 5 marbles = 11.10 + 8.40
5 stickers + 5 marbles = 19.50 --- (3)

(3) _{÷ 5}
5 stickers + 5 marbles = 19.50
1 sticker + 1 marble = 19.50 ÷ 5
1 sticker + 1 marble = 3.90 --- (4)

(b)
(2) - (4)
(1 sticker + 4 marbles) - (1 sticker + 1 marble) = 8.40 - 3.90
1 sticker - 1 sticker + 4 marbles - 1 marble = 4.50
3 marbles = 4.50
1 marble = 4.50 ÷ 3 = 1.50

Cost of 1 marble = $1.50

(c)
Substitute 1 marble = 1.50 into (4).
1 sticker + 1 marble = 3.90
1 sticker + 1.50 = 3.90
1 sticker = 3.90 - 1.50 = 2.40

Cost of 1 sticker = $2.40

(d)
(4) _{x 8}
1 sticker + 1 marble = 3.90
8 x (1 sticker + 1 marble) = 8 x 3.90
8 stickers + 8 marbles = 31.20

Cost of 8 stickers and 8 marbles = $31.20

Answer(s): (a) $3.90; (b) $1.50; (c) $2.40; (d) $31.20