#### Answer

240

#### Work Step by Step

We first combine this into one square root:
$4 \times 2 \sqrt {10\times 90} = 8 \sqrt {900}$
We see if any of the factors of a radical are perfect squares (meaning that their square root will be an integer) to see if the radical is in its most simplified form. We see that 900 is a perfect square, so we know that we can simplify:
$8 \sqrt {900}=8 \times 30=240$