Adam pays $9.40 for 4 marbles and 3 stickers.
A marble costs $1.30 more than 1 sticker.
What is the cost of 2 marbles and 4 stickers?
Choose the cheaper item to be 1 u.
1 marble costs $1.30 more than 1 sticker.
The cheaper item is the sticker.

Cost of the sticker = 1 u
Cost of the marble = 1 u + 1.30

Cost of 4 marbles = 4 x (1 u + 1.30) = 4 u + 5.20
Cost of 3 stickers = 3 u

Total cost of 4 marbles and 3 stickers
= 4 u + 5.20 + 3 u
= 4 u + 3 u + 5.20
= 7 u + 5.20

7 u + 5.20 = 9.40
7 u = 9.40 - 5.20
7 u = 4.20

1 u = 4.20 ÷ 7 = 0.60

Cost of 2 marbles and 4 stickers
= 2 x (1 u + 1.30) + 4 u
= 2 u + 2.60 + 4 u
= 2 u + 4 u + 2.60
= 6 u + 2.60
= 6 x 0.60 + 2.60
= 3.60 + 2.60
= $6.20

Answer(s): $6.20