Question

http://prntscr.com/5ccpmg

Answer 1

Square it \[
(6\sqrt7)^2= 36(7)=252
\]

Answer 2

\[
15^2 =225 \\16^2=256
\]

Answer 3

So it's really close to \(16\)

Answer 4

And the best interval near \(16\) is D.