we can find the answer to this problem by thinking about it logically for a minute:
we know that she assigned "x" homework problems on Monday, so,
x=Monday
we also know that she assigned 13 more problems on Tuesday, so,
13=Tuesday
over the course of the two days she assigned a total of 23 homework problems.
to get the answer of how many problems she assigned on Monday, we have to do the total number of problems she assigned(23) minus the number of problems we know she assigned on Tuesday(13), so,
23-13=10
she assigned 10 problems on Monday.
