80 plus what equals 9?

This is how to calculate "80 plus what equals 9?" In other words, 80 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:

80 + what = 9

To solve this equation, we first add -80 to each side of the equal sign like this:

80 - 80 + what = 9 - 80

Then, we do the calculation to get the answer to "80 plus what equals 9?" as follows:

What = -71

The answer to "80 plus what equals 9?" is -71. You know this answer is correct because 80 plus -71 equals 9.

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80 plus what equals 10?
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