Solution(By Examveda Team)
$$\eqalign{
& = \frac{2}{5}{\text{A}} + 40 = \frac{2}{7}{\text{B}} + 20 \cr
& \Rightarrow \frac{2}{7}{\text{B}} = \frac{2}{5}{\text{A}} + 20 \cr
& \Rightarrow {\text{B}} = \frac{7}{2}\left( {\frac{2}{5}{\text{A}} + 20} \right) \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\, = \left( {\frac{7}{5}{\text{A}} + 70} \right) \cr
& {\text{And,}} \cr
& = \frac{2}{5}{\text{A}} + 40 = \frac{9}{{17}}{\text{C}} + 10 \cr
& \Rightarrow \frac{9}{{17}}{\text{C}} = \frac{2}{5}{\text{A}} + 30 \cr
& \Rightarrow {\text{C}} = \frac{{17}}{9}\left( {\frac{2}{5}{\text{A}} + 30} \right) \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{34}}{{45}}{\text{A}} + \frac{{170}}{3} \cr
& = {\text{A}} + {\text{B}} + {\text{C}} = 600 \cr
& \Rightarrow {\text{A}} + \left( {\frac{7}{5}{\text{A}} + 70} \right) + \left( {\frac{{34}}{{45}}{\text{A}} + \frac{{170}}{3}} \right) = 600 \cr
& \Rightarrow \frac{{142{\text{A}}}}{{45}} = 600 - \frac{{380}}{3} \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{1420}}{3} \cr
& \Rightarrow {\text{A}} = \frac{{1420}}{3} \times \frac{{45}}{{142}} \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\, = 150 \cr} $$
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