10n + 9 = 89
solving simple equations

So subtract 9 on both sides
10n=80
Divide by 10 on both sides
n=8

So, our goal is to solve for n, right? In that case, 10 and 9 are keeping n from being by itself. Typically, we start by moving added or subtracted values first, rather than multiplication and division, but that isn't a strict rule. In this case, it is true though. So, how would we move 9, since it's being added? Well, if we subtract 9 from both sides, it'll disappear. I'll show this.

10n + 9 = 89

Subtract by 9

10n + 9 - 9 = 89 - 9

(Remember, for an equation, if we do something to one side, we have to do it to the other to maintain equality)

This further simplifies to:

10n = 80

If you're ever unsure if what you're doing is "correct", say you thought that you should've added 9, do whatever you thought you should do, and see if it actually candles the value you wanted to get rid of. If we had added 9, it wouldn't have gotten rid of 9, only increased it.

So! Now the only thing keeping us from having n by itself is that nasty 10. We see that n is being multiplied by 10, so we'll have to divide to get rid of it. Same logic from before can assist you in knowing what to do. Actually divide, and see if it cancels. If it doesn't, you haven't done the right operation.

10n/10 = 80/10

10/10 is 1, so we have 1×n or just N. 80/10 is 8.

n= 8

There you go! let me know if this doesn't make sense. I'd be happy to elaborate.

Subtracting is the opposite of adding

The answer to your question is 1/9