How do you calculate the square root of 20 plus the square root of 5?

$\sqrt{20} + \sqrt{5} = 3 \sqrt{5}$

Explanation:

$\sqrt{20} + \sqrt{5}$
$20 = 4 \times 5$
$\sqrt{20} = \sqrt{4 \times 5}$
$\sqrt{4 \times 5} = \sqrt{4} \times \sqrt{5}$
$\sqrt{20} = \sqrt{4} \times \sqrt{5}$
$\sqrt{4} = 2$
$\sqrt{20} = 2 \times \sqrt{5}$
$2 \times \sqrt{5} = 2 \sqrt{5}$
$\sqrt{20} = 2 \sqrt{5}$
$\sqrt{20} + \sqrt{5} = 2 \sqrt{5} + \sqrt{5}$
$2 \sqrt{5} + \sqrt{5} = 3 \sqrt{5}$
$\sqrt{20} + \sqrt{5} = 3 \sqrt{5}$