The solution is m=40. you just needed to divide 7 by 56, then you get 8. after that you multiply 8 by 5.
The side lengths are congruent, because the triangle is only being moved
has divergence
so that by the divergence theorem, the flux of through is the integral of over the interior of (call it ):
is a tetrahedron in the first quadrant defined by the set
(and this is by no means the only way to define )
Then the integral over is