What is parallogram law?

The Parallelogram law states that the the resultant of two vector quantities represented in magnitude, direction, and sense by two adjacent sides of a parallelogram both of which are directed toward or away from their point of intersection is the diagonal of the parallelogram through that point.

If two vectors acting simultaneously on a particle are represented in magnitude and direction by the two adjacent sides of a parallelogram drawn from a point, then their resultant is completely represented in magnitude and direction by the diagonal of that parallelogram drawn from that point.

v=ir = 3x15 =45 v

the answer is f1 and d2 because if you put equal force on those two points the beam would balance trust me on this