5 stickers and 1 marble cost $25.60.
1 sticker and 5 marbles cost $12.80.

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)
5 stickers + 1 marble = 25.60 --- (1)
1 sticker + 5 marbles = 12.80 --- (2)

(1) + (2)
6 stickers + 6 marbles = 25.60 + 12.80
6 stickers + 6 marbles = 38.40 --- (3)

(3) _{÷ 6}
6 stickers + 6 marbles = 38.40
1 sticker + 1 marble = 38.40 ÷ 6
1 sticker + 1 marble = 6.40 --- (4)

(b)
(2) - (4)
(1 sticker + 5 marbles) - (1 sticker + 1 marble) = 12.80 - 6.40
1 sticker - 1 sticker + 5 marbles - 1 marble = 6.40
4 marbles = 6.40
1 marble = 6.40 ÷ 4 = 1.60

Cost of 1 marble = $1.60

(c)
Substitute 1 marble = 1.60 into (4).
1 sticker + 1 marble = 6.40
1 sticker + 1.60 = 6.40
1 sticker = 6.40 - 1.60 = 4.80

Cost of 1 sticker = $4.80

(d)
(4) _{x 8}
1 sticker + 1 marble = 6.40
8 x (1 sticker + 1 marble) = 8 x 6.40
8 stickers + 8 marbles = 51.20

Cost of 8 stickers and 8 marbles = $51.20

Answer(s): (a) $6.40; (b) $1.60; (c) $4.80; (d) $51.20