Apparently, you're to assume that the amount of food is supposed to be proportional to weight. If x is the amount of food for the 26-pound dog, then ...
cups/weight = (1 5/8)/14 = x/26
Multiplying by 26 we have ...
x = (26)(13/8)/14 = 338/112 . . . cups
x = 3 1/56 cups ≈ 3.02 cups
About 3.02 cups of the same type of food should be fed to a 26-pound dog.
