Three masses m,2m and 3m are moving in x - y plane with speed 3u,2u and u respectively as shown in figure . The three masses collide at the same point at P and stick together .The velocity of resulting mass will be :

Question

$(a)\;\large\frac{u}{12} (\normalsize \hat{i}+\normalsize \sqrt{3}\hat{j})\qquad(b)\;\large\frac{u}{12} (\normalsize \hat{i}-\normalsize \sqrt{3}\hat{j})\qquad(c)\;\large\frac{u}{12} (-\normalsize \hat{i}+\normalsize \sqrt{3}\hat{j})\qquad(d)\;\large\frac{u}{12} (-\normalsize \hat{i}-\normalsize \sqrt{3}\hat{j})$