Below are some sale prices for soda .Which offers the best price ?

a. 6 for $1.75
b.8 for $1.90
c.12 for $3.15
d.30 for $7.50

the prices per can are:

1.75/6 1.90/8 3.15/12 7.50/30
.29 .23 .26 .25

so, ...