Answer:
So the final answer is

Step-by-step explanation:
Radicals:
In mathematics, a radical expression is defined as any expression containing a radical (√) symbol. Many people mistakenly call this a 'square root' symbol, and many times it is used to determine the square root of a number. However, it can also be used to describe a cube root, a fourth root, or higher.
The given expression is

Now take common radical out so we will get

Now add the Parenthesis part.

So the final answer is

First of all, this shouldn't be in high school category.
Second, 20 divided by 2 is 10. Dividing is like subtraction. You would subtract 20 by 2, and you would find that after 10 times, you will get to zero.
Step-by-step explanation:
=2√-28
=2√4×7×-1
=2(2)√7×-1
=4i√7 (i=√-1)
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The answer is 11 so C=11.