solution for balanis problem

An antenna has a beam solid angle that is equivalent to a trapezoidal patch
(patch with 4 sides, 2 of which are parallel to each other) on the surface of
a sphere of radius r. The angular space of the patch on the surface of the
sphere extends between π/6 ≤ θ ≤ π/3(30◦ ≤ θ ≤ 60◦) in latitude and π/4 ≤φ ≤ π/3
(45◦ ≤ φ ≤ 60◦) in longitude. Find the following:
(a) Equivalent beam solid angle [which is equal to number of square radians/
steradians or (degrees)2] of the patch [in square radians/steradians
and in (degrees)2 ].
a] Exact.
b] Approximate using 2A = 34 · 3P = (θ2 − θ1) · (φ2 − φ1). Compare
with the exact.

Does anyone know the solution of this problem?

Thanks in advance