Answer:
A. 2.10b + 12.99 = 21.39; 4 bottles
Step-by-step explanation:
The b represents bottles of water, at the end of the equation. If each bottle is $2.10, and there were 4 bottles brought, $2.10 * 4 = $8.40, and $8.40 + $12.99 is $21.39.
