Explanation:
it is really easy.
let's imagine an even simpler scenario :
2 units cost $4.
how much is 1 unit ?
I am sure you know what to do.
it is also similar to "there are 4 slices of pizza for 2 people - how many slices does every person get ?"
we divide the whole by the number of parts we need to split it into.
4/2 = 2
one unit costs $2, every person gets 2 slices.
now, in the same way we approach the given problem :
48 cans cost $12
how much is 1 can ?
the whole is $12.
and we need to split this into 48 parts.
so,
1 can = 12 / 48 = 1/4.
$1/4 = a quarter (hence the name) = $0.25
so, 1 can (and that is the meaning of "unit rate") costs $0.25.