Answer
$24\sqrt {15}$
Work Step by Step
Make the square roots positive by creating an imaginary number outside them. Then multiply the terms in the parentheses and turn $i^2$ into $-1$. Then simplify the radical.
$(3\sqrt {-5})(-4\sqrt {-12})$
$(3i\sqrt 5)(-4i\sqrt {12})$
$-12i^2\sqrt {60}$
$12\sqrt {60}$
$24\sqrt {15}$
