Hi Mary,

You can do this by trial and error but I think you are expected to use algebra.

There are two unknown numbers so give them names. I am going to call them $m$ and $n.$ The first requirement is that

One number is 9 more than the other number.

Algebraically this says that

\[m = n + 9.\]

The second requirement is that

The sum of the numbers is 45.

Write an algebraic expression for this requirement. In this expression replace $m$ using $m = n + 9.$ Solve for $n$ and then you know that $m = n + 9.$