I'll assume those are squares. We know D is an identity:
Dividing through by
That's A.
Dividing the original through by
Not quite B, wrong sign on tangent.
C has the wrong sign on cosine squared as well.
Identities: A & D
1809.56
just plug it in the surface area formula of a sphere and do the math
Area = length x width
21 = length x 5
length = 21/5 = 4.2
The length is inversely proportional to the width because as the length increases the width reduces and vice-versa