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Here is the solution of your asked query:
$$\begin{gathered} \mathrm{Let} \mathrm{monthly} \mathrm{income} \mathrm{of} \mathrm{Sunil} \mathrm{be} \mathrm{Rs}.\mathrm{x} \\ \mathrm{Money} \mathrm{spent} \mathrm{on} \mathrm{Children}\text{'}\mathrm{s} \mathrm{education} = 10\% \mathrm{of} \mathrm{x} = \mathrm{x}\times \frac{10}{100}=\frac{10\mathrm{x}}{100} \\ \mathrm{Money} \mathrm{invested} \mathrm{on} \mathrm{shares} = 12\% \mathrm{of} \mathrm{x}=\mathrm{x}\times \frac{12}{100}=\frac{12\mathrm{x}}{100} \\ \mathrm{Money} \mathrm{deposited} \mathrm{in} \mathrm{a} \mathrm{bank}=8\% \mathrm{of} \mathrm{x}=\mathrm{x}\times \frac{8}{100}=\frac{8\mathrm{x}}{100} \\ \mathrm{So}, \mathrm{amount} \mathrm{remaining} = \mathrm{x}-\left(\frac{10\mathrm{x}}{100}+\frac{12\mathrm{x}}{100}+\frac{8\mathrm{x}}{100}\right)=\frac{70\mathrm{x}}{100} \\ \mathrm{Amount} \mathrm{spent} \mathrm{for} \mathrm{daily} \mathrm{expenditure} = 25\% \mathrm{of} \frac{70\mathrm{x}}{100} = \frac{25}{100}\times \frac{70\mathrm{x}}{100}=\frac{7\mathrm{x}}{40} \\ \mathrm{So} \mathrm{total} \mathrm{amount} \mathrm{left} \mathrm{after} \mathrm{investment} \mathrm{and} \mathrm{expenditure} = \mathrm{x}-\left(\frac{10\mathrm{x}}{100}+\frac{12\mathrm{x}}{100}+\frac{8\mathrm{x}}{100}+\frac{7\mathrm{x}}{40}\right) = \frac{105\mathrm{x}}{200} \\ \mathrm{So} \mathrm{we} \mathrm{have}; \\ \frac{105\mathrm{x}}{200}=39900 \\ \Rightarrow \mathrm{x}=\frac{39900\times 200}{105}=76000 \\ \mathrm{Therefore}, \mathrm{monthly} \mathrm{income} \mathrm{of} \mathrm{Sunil} \mathrm{is} \mathrm{Rs}.76000 \end{gathered}$$
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