Let's define first the variables.
let H be the number of bags of the type that cost 3.25 and P the number of bags of the type that cost 2.75.
since they sold a total of 156 bags we have that H+P=156
and from the other condition we obtain 3.25H+2.75P=455
now we can solve the system of equations.
from the first equation H=156-P
substituing the previous equality in the second one we obtain:





now that we have P, we can replace it in the first equation obtaining that H=50
then the answer will be that they sold 50 bags of $3.25 and 106 bags of $2.75