You just have to ignore the first thing it asks for, and then write out what it's saying. Since it's asking for the difference, you have to subtract what it tells you to. In this case they are asking for you to subtract 7 times a number from 18 which is the same as writing 18-7n. Then, go back to the first thing it asks for and that wants you to add one. You now have this: 18-7n+1. Now all you have to do is set it equal to whatever it asks you for, which is -9. The final product should look like this:
18-7n+1= -9
I hope this helps and if you could let me know if I helped, that would be greatly appreciated!
