You can continue the way you started by summing moments about any point...sum of .clockwise moments equals sum of anti clockwise moments...and be sure to include the moments from the x component of the forces. It is best to sum moments about one of the forces to reduce calculation effort. Your dimensions horizontally are not clear..is it 20 mm right. to the application of the first force and 10 mm left to the last force? All forces are applied at the shown points on the frame. Don't forget the weight resultant acts at midpoint of beam, so be sure to get the correct distance of it to the point you are summing moments about. I suggest summing moments about the left force. Now for example what is the moment about that point from the horizontal component of the last force? Is it clockwise or anti clockwise?