6 plus what equals 21?

This is how to calculate "6 plus what equals 21?" In other words, 6 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:

6 + what = 21

To solve this equation, we first add -6 to each side of the equal sign like this:

6 - 6 + what = 21 - 6

Then, we do the calculation to get the answer to "6 plus what equals 21?" as follows:

What = 15

The answer to "6 plus what equals 21?" is 15. You know this answer is correct because 6 plus 15 equals 21.

Plus What Equals Calculator
Here you can calculate a similar problem:

6 plus what equals 22?
Do you think you can solve a similar problem on your own? Try to figure out the next problem on our list and then go here to check the answer.