Answer:
A large box costs $19.
A small box costs $16
Explanation:
s = cost of a small box
l = cost of a large box
From the problem, we can make these two formulas.
# of small boxes + # of large boxes = total cost
10s + 3l = 217
3s + 12l = 276
Rewrite one equation for either s or l:
3s = 276 - 12l
s = 92 - 4l
Now use substitution to solve. Plug the s equation from above into
10s + 3l = 217
10 (92 - 4l) + 3l = 217
920 - 40l + 3l = 217
-37l = -703
l = 19
This is the cost of a large box.
Plug l into:
s = 92 - 4l
s = 92 - 4(19)
s = 16
This is the cost of a small box.