The unit price of an 8 pound bag of dog food for $7.40 is:
$7.40/ 8 pounds= $0.93/pound.
The unit price of a 4 pound bag of dog food for $5.38 is:
$5.38/ 4 pounds= $1.35/pound.
Because $1.35/pound > $0.93/pound, an 8 pound bag of dog food for $7.40 is a better deal.
Hope this helps~