Solution:
If the price of the 12.6 L bottle of shampoo is $4.99 then, the unit rate is

that is 2.53L per $1.
on the other side, if the price of the 10.2 L bottle of shampoo is $3.49 then, the unit rate is

that is 2.92 L per $1.
notice that per $1, we have that:

So we get more amount of shampoo for 10.2 L bottle of shampoo at a price $3.49.