Centre of gravity of this system of particles

[pinnacleprouk]

Homework Statement

Find the centre of gravity of this system of particles

Homework Equations

attached image showing diagram

http://www.zshare.net/image/7209360586277b98/

The Attempt at a Solution

Taking moments about a, 4*0+6*30 = 184 then not sure

Any help is greatly appreciated

Thanks in advance

 

[HallsofIvy]

Don't worry about moments- take a "weighted" average of the components. Taking the 4 kg mass on the left to be at (0, 0), the 6 kg mass is at (30, 0) and the 8 kg mass at (30, -14). The x-coordinate of the center of mass will be at
$$\frac{4(0)+ 6(30)+ 8(30)}{4+ 6+ 8}$$
and the y-coordinate will be
$$\frac{4(0)+ 6(0)+ 8(-14)}{4+ 6+ 8}$$

 

[pinnacleprouk]

Thanks for the reply, ok so I get 23.33 for x and -6.22 for y,

Providing I have calculated the sums correctly,
the minus is throwing me off in locating the centre?

Thanks again!