Answer:
3 postcards
Step-by-step explanation:
So the question says that Brenna bought 4 packs of 12 postcards, which is the same as 4x12.
4x12=48, so Brenna bought 48 postcards.
It says that she only needed 45, so we can subtract 45 from 48.
48-45=3
Brenna had three postcards left over.
Hope this helped you!