Replace the force system by an equivalent resultant force an

Replace the force system by an equivalent resultant force and couple moment at point O.

Solution

Moment due to 455N -> 455*cos(theta)*2 = +2*455*12/13 = +840Nm (Anticlockwise)
Moment due to 600n -> 600*cos(60)*0.75 + 600*sin(60)*2.5 = 225 + 1299.03 = 1524 Nm
Net Moment = 2364 N

x - component of force = -455*cos(theta) + 600cos(60) = -455*(12/13) + 300 = -120N *(along -ve x axis)
y - component of force = 455*sin(theta) - 600*sin(60) = 455*(5/13) - 519.615 = -344N (along -ve y axis)
Net Force = sqroot(120^2 + 344^2) = 364.32N
Angle made with x axis = arctan(-344/-120) = 250.76 anti-clockwise direction