Answer:
D. 8 bottles
Explanation:
one bottle of one is obviously $6.50
one bottle of two : $12.50 (1/2) = $6.25
one bottle of four: $26.00 (1/4) = $6.50
one bottle of six: $30.00 (1/6) = $5.00
one bottle of eight: $38.00 (1/8) = $4.75
8 bottles is the best buy