30 plus what equals 9?

This is how to calculate "30 plus what equals 9?" In other words, 30 plus a number equals 9. What is that number? We start by converting this word problem into an equation where "what" is what we want to solve:

30 + what = 9

To solve this equation, we first add -30 to each side of the equal sign like this:

30 - 30 + what = 9 - 30

Then, we do the calculation to get the answer to "30 plus what equals 9?" as follows:

What = -21

The answer to "30 plus what equals 9?" is -21. You know this answer is correct because 30 plus -21 equals 9.

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30 plus what equals 10?
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