debt to equity ratio

i am a PhD student. I have a question to solve but it is still a problem for me. The question is as follows. Determine the optimal debt-equity ratio in case of the following valuation model (where 'V' is the value of firm, 'S' is number of shares adn 'B' is number of bonds. Suppose shares are being traded at Rs.10/- each and bond at Rs.50/- each. V = 25 S.60 B.40 The .60 and .40 are superscript. Is there any one who can solve it for me

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