Simplify 3 square root of ab^2-b square root of a

$3 \sqrt{a b^{2}} - b \sqrt{a}$

Simplify each term.

Reorder $a$ and $b^{2}$ .

$3 \sqrt{b^{2} a} - b \sqrt{a}$

Pull terms out from under the radical.

$3 b \sqrt{a} - b \sqrt{a}$

Subtract $b \sqrt{a}$ from $3 b \sqrt{a}$ .

$2 b \sqrt{a}$