Ialways get terribly confused on these, show work?

I'll try my best to explain this.

First off, and equilateral triangle is just a triangle with 3 equal sides.

For the

You just plug in the numbers you're given (m=2 and n=121) So your equation would look like this

Which means the square root of 121. So really the question is simply asking for

Your answer would be 11.

The answer should be c.