#### Answer

$-126a \sqrt a$

#### Work Step by Step

$-9 \times \sqrt 4 \times \sqrt (7a^{2}) \times \frac{1}{3} \times \sqrt 9 \times \sqrt 7a $
*** $ \sqrt 4$ = 2 because $2 \times 2$ = 4
*** $ \sqrt a^{2}$ = a because $a \times a = a^{2}$
*** $ \sqrt 9$ = 3 because $3 \times 3$ = 9
$-9 \times 2 \times a \times \sqrt 7 \times \frac{1}{3} \times 3 \times \sqrt 7a $
We multiply the constants together and the numbers in the square root rogether
$-18a \times \sqrt 49a$
49 is a perfect square because 7 x 7 = 49
$-18a \times 7 \times \sqrt a$
$-126a \times \sqrt a$
$-126a \sqrt a$