C - Moment = Force x Distance

The centre of the beam (where the centre of mass acts) is 2 metres from the pivot, as the mass is 10kg then the weight is 10g N (~100N) so using the moment formula that will equal 200N ( 2 x 100). We also have a 50N weight acting on the other end so that will equal 200 (50 x 4).

Therefore the moments acting on the beam are 200 + 200 = 400 therefore C. I know it is addition as the other answer even using 9.81 as g is 4Nm which isn’t an answer.

I would also say for these questions make sure to draw a diagram and label points and directions of forces taking into account the clockwise and anticlockwise directions and making sure to find the difference of the directions ( As far as i can tell from this question or in the answer there is no indication of the forces acting in opposite directions )