Answer:
Nolan correctly identified the square numbers before and after 18.
The square roots of them are 4 and 5.
Clearly, square root of 18 should lie between 4 and 5 only.
He, then carefully squared 4.1, 4.2, 4.3 etc. and identified that 4.3 squared is nearer to 18.
Since, Nolan is finding estimated square root, his steps are cool and he didn't make any error.
24! 2 plus 4 is 6 and 6 times 4 for the scale factor
The surface (call it
) is a triangle with vertices at the points



Parameterize
by

with
and
. Take the normal vector to
to be

Then the flux of
across
is


