Answer
$5\sqrt {21}$
Work Step by Step
Step 1: $\sqrt {15}\times\sqrt {35}$
Step 2: $\sqrt {3\times5}\times\sqrt {5\times7}$
Step 3: $\sqrt 3\times\sqrt 5\times\sqrt 5\times\sqrt 7$
Step 4: $\sqrt 3\times(\sqrt 5\times\sqrt 5)\times\sqrt 7$
Step 5: $\sqrt 3\times(5)\times\sqrt 7$
Step 6: $5\times\sqrt 3\times\sqrt 7$
Step 7: $5\sqrt {21}$
