We calculate for the price per unit dimension of the given items. Since these are given in ounce.
a. The unit price of the given item is,
$2.53 / 46 = $0.055/ ounce
b. The unit price of the given item is,
$4.5 / (6)(10) = $0.075/ounce
The price of a is basically smaller compared to b. Hence, the best buy would be a.