Answer
$$=3\sqrt{5}-1$$
Work Step by Step
Simplifying the expression using the rules of radicals, we find:
$$ \left(1+\sqrt{5}\right)\left(4-\sqrt{5}\right)\\ 1\cdot \:4+1\cdot \left(-\sqrt{5}\right)+\sqrt{5}\cdot \:4+\sqrt{5}\left(-\sqrt{5}\right)\\ =3\sqrt{5}-1$$