Find the distance of the center of gravity from the origin. Answer in units of m

Three particles are located in a coordinate system as shown in the figure below:
http://oi42.tinypic.com/2yy2yz4.jpg

The mass 3 kg is located at the origin, the mass 7 kg is located on the x coordinate, and the mass 8 kg is located on the y coordinate.

Find the distance of the center of gravity from the origin. Answer in units of m

Let the center of mass be at x,y and its mass is ( 8+7+3) = 18kg

Take the moment of the masses along the x direction

8*0 + 3*0 + 7*8 = 18 x

x = 3.1m

Take the moment of the masses along the y direction
8*7 = 18 y
y = 3.1m

Distance from the origin = √ (2*3.1^2) = 3.1*√ 2 = 4.38
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