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