66 plus what equals 21?

This is how to calculate "66 plus what equals 21?" In other words, 66 plus a number equals 21. What is that number? We start by converting this word problem into an equation where "what" is what we want to solve:

66 + what = 21

To solve this equation, we first add -66 to each side of the equal sign like this:

66 - 66 + what = 21 - 66

Then, we do the calculation to get the answer to "66 plus what equals 21?" as follows:

What = -45

The answer to "66 plus what equals 21?" is -45. You know this answer is correct because 66 plus -45 equals 21.

Plus What Equals Calculator
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66 plus what equals 22?
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