Adam pays $17.50 for 3 marbles and 4 beads.
A marble costs $2.10 more than 1 bead.
What is the cost of 4 marbles and 3 beads?
Choose the cheaper item to be 1 u.
1 marble costs $2.10 more than 1 bead.
The cheaper item is the bead.

Cost of the bead = 1 u
Cost of the marble = 1 u + 2.10

Cost of 3 marbles = 3 x (1 u + 2.10) = 3 u + 6.30
Cost of 4 beads = 4 u

Total cost of 3 marbles and 4 beads
= 3 u + 6.30 + 4 u
= 3 u + 4 u + 6.30
= 7 u + 6.30

7 u + 6.30 = 17.50
7 u = 17.50 - 6.30
7 u = 11.20

1 u = 11.20 ÷ 7 = 1.60

Cost of 4 marbles and 3 beads
= 4 x (1 u + 2.10) + 3 u
= 4 u + 8.40 + 3 u
= 4 u + 3 u + 8.40
= 7 u + 8.40
= 7 x 1.60 + 8.40
= 11.20 + 8.40
= $19.60

Answer(s): $19.60