number: n
square of number: n^2
sum of n and n^2 is n+n^2=20
Rewriting this equation, we get n^2+n-20=0 = (n+5)(n-4) = 0
Then n+5=0 and n-4=0, so n = -5 and n = 4.
You must check both results. It could happen that both are correct, or that only one is correct.
