Wires $W_1$ and $W_2$ are made of same material having the breaking stress of $1.25 \times 10^9 \mathrm{~N} / \mathrm{m}^2 . W_1$ and $W_2$ have cross-sectional area of $8 \times 10^{-7} \mathrm{~m}^2$ and $4 \times 10^{-7} \mathrm{~m}^2$, respectively. Masses of 20 kg and 10 kg hang from them as shown in the figure. The maximum mass that can be placed in the pan without breaking the wires is $\_\_\_\_$ kg. (Use $\mathrm{g}=10 \mathrm{m} / \mathrm{s}^2$ )