(x^2+x-20)/(x-4) long devision
The numerator can be factored as \((x+5)(x-4)\) so you have;
\(\frac{x^2+x-20}{x-4}\rightarrow\frac{(x+5)(x-4)}{x-4}\rightarrow x+5\)
.
(x^2+x-20)/(x-4)
x + 5
x - 4 [ x^2 + x - 20 ]
- [ x^2 -4x ]
5x - 20
- [ 5x - 20 ]
0