Answer:
$8.40
Explanation:
Shelley sells 5 bone-shaped treats for $3.50
We need the proportion of how many dollars per treat, so we divide it.
The cost of per bone-shaped treats =

= $0.70
Since She sells one bone-shaped treat in $0.70
Therefore, she should charge for a package of 12 treats = 0.70 × 12
=$8.40
Shelley should charge $8.40 for 12 treats.