#### Answer

$\frac{i}{3}$

#### Work Step by Step

Step 1: $\frac{\sqrt (-8)}{\sqrt (72)}$
Step 2: $\frac{\sqrt (-1\times8)}{\sqrt (8\times9)}$
Step 3: $\frac{\sqrt (-1)\times\sqrt 8}{\sqrt 8\times\sqrt 9}$
Step 4: Removing $\sqrt 8$ as it is common to both numerator and denominator, $\frac{\sqrt (-1)}{\sqrt 9}$
Step 5: $\frac{\sqrt (-1)}{\sqrt 9}=\frac{i}{3}$