In each case, divide the cost by the weight to find the cost per pound.
The unit rate is dollars per pound.
Sand a: $5/(60 lb) = 0.08333 $/lb
Sand b: $12/(150 lb) = 0.08 $/lb
A. Sand a is 0.08333 $/lb
B. Sand b is $0.08 $/lb
Sand b has a lower unit rate.
Sand b is is the better value.
If you buy the same amount of sand a and sand b, you will spend less money per pound of sand by buying sand b.