Three masses are placed on the x -axis: 300 g at origin, 500 g at x=40 cm and 400 g at x=70 cm. The distance of the centre of mass from the origin is:

Three masses are placed on the $\displaystyle x$-axis : $\displaystyle 300$ g at origin, $\displaystyle 500$ g at $\displaystyle x=40 \mathrm{~cm}$ and $\displaystyle 400$ g at $\displaystyle x=70 \mathrm{~cm}$. The distance of the centre of mass from the origin is :