If 5 is added to the square of a number, the result is 21. Find the number.

x(x+5)=21

I think the answer is 4,-4 but do not really know how to work the problem out! Please help. And thank you in advanced. I am a bit frustrated...

The way I did it is...21-5 is 16, the square of 16 is 4. which makes it 4, -4