$$
K_1 = \frac{1}{10};\space K_2 = \frac{1}{15}
$$
$$
M_1 = \frac{K_1}{K_1 + K_2}\times M = 0.6\times 20.3 = 12.2
$$
$$
M_2 = \frac{K_2}{K_1 + K_2}\times M = 0.4\times 20.3 = 8.1
$$

Alternatively,

$$
M_2 = M - M_1 = 20.3 - 12.2 = 8.1
$$
Simplified:

$$
M_1 = \frac{M}{L_1+L_2}\times L_2
$$
$$
M_2 = \frac{M}{L_1+L_2}\times L1
$$