To add these two fractions, you must first get them having common denominators. Notice that the denominators are factors of each other. 9*5=45. So you can multiply the first fraction by 5/5 and get common denominators.
And when multiplying fractions, you just multiply across so your new fractions are:
35/45 - 22/45
Now that you have common denominators, you can just subtract across the top.
This gives you a fraction of 13/45
13 and 45 are not factors of each other so it cannot be simplified. That means you are done!