A uniformly thick plate in the shape of an arrow head has dimensions as shown. The centre of mass lies at a point
 

COM of an isosceles triangle is on median and  h/3 above the base.

So, COM of bigger triangle is 3 cm from base and that of lower (hollow ) triangle is 1 cm. Calculating COM of the system. (hollow triangle is considered as negative mass )

From the base i.e. , 1 cm to right of O.X component of centre of mass of $∆$OAB

$\left(\frac{3\left(3\mathrm{m}\right)+1(-\mathrm{m})}{2\mathrm{m}}\right)=4$
4 cm from origin, i.e 1cm to the right of O