Sam pulls with 120 Newtons of force at 30° and Alex pulls with 100 Newtons of force at 45° as?

Are you finding resultant force ? Assuming they pulls in opposit direction ,

Fx = 120cos30 - 100cos45
Fy = 120sin30.+ 100sin45

Resultant force = square root of Fx^2 + Fy^2 .
Angle = Tan^-1 (Fy/Fx)

The key to this question is to resolve the forces parallel to x and y axis . By drawing a triangle and Phytagoras Theorem , we assume the Hypotenuses (h) is the forces and to find force parallel to x axis , we have to cosines the force to the angle as we are finding Adjacent (a) , Similarly to find Fy , we have to sines the force to the angle as we are finding the opposite (o) .

Add force in same direction and minus forces moving in the opposite directions.
From a Fellow Engineers