a. 25 ounces of potato chips for $3.49 => $ 3.49 / 25 ounce =
= $ 0.1396 / ounce < ---- unit rate
b. 45 ounces of potato chips for $4.79 => $ 4.79 / 45 ounces =
= $ 0.1064 / ounce. <---- unit rate
So, the answer is the unit rates are different, being the choice b, the lowest price per ounce.