21 plus what equals 4?

This is how to calculate "21 plus what equals 4?" In other words, 21 plus a number equals 4. What is that number? We start by converting this word problem into an equation where "what" is what we want to solve:

21 + what = 4

To solve this equation, we first add -21 to each side of the equal sign like this:

21 - 21 + what = 4 - 21

Then, we do the calculation to get the answer to "21 plus what equals 4?" as follows:

What = -17

The answer to "21 plus what equals 4?" is -17. You know this answer is correct because 21 plus -17 equals 4.

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

21 plus what equals 5?
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.