Ask Me Help Desk - Radical expression (adding and subtracting)

You can do them in a calculator, each one, and do the remaining calculations... or you mean simplifying? Then here we go!

$\sqrt{99}$

divide by a square number you know, 9. The square root of 9 is 3. ok:

$\sqrt{99} = \sqrt{11\times9} = \sqrt{9} \times \sqrt{11} = 3 \times \sqrt{11}=3\sqrt{11}$

$\sqrt{63}$

Same thing:
$\sqrt{63} = \sqrt{7\times9} = \sqrt9 \times \sqrt7 = 3 \times \sqrt7=3\sqrt7$

and

$\sqrt{144}$

is 12, giving;

$3\sqrt{11} + 3\sqrt7 - 12$

Then you can further simplify, $3(\sqrt{11} + \sqrt7) - 12$