I belive the answer is the 3rd one
We can separate the shape into a rectangle and a square
the area of the rectangle :

the area of the square:

the area of the whole shape:

hope this helps
Answer:
it decended 239 feet per minute
Step-by-step explanation:
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


