Combined mean of two series $x_1\: and \: x_2$ when $x_1 = 210,\: x_2 = 150, \: n_1=50, \: n_2=100$ is

Question

$\begin {array} {1 1} (A)\;150 & \quad (B)\;160 \\ (C)\;170 & \quad (D)\;180 \end {array}$