Explain the concept of Spheres of Influence:

Sphere of influence, in international politics, the claim by a state to exclusive or predominant control over a foreign area or territory. The term may refer to a political claim to exclusive control, which other nations may or may not recognize as a matter of fact, or it may refer to a legal agreement by which another state or states pledge themselves to refrain from interference within the sphere of influence.

It’s letter b because the area of the trapezoid is 72