A man decides to deposit a certain amount which will be equivalent to $P28,000$ with today's purchasing power of the peso on his son's $18$th birthday when he will start his college education. If today is his son's $5$ th birthday and the bank pays $5\mathrm{.}5\%$ interest compounded annually but the rate of inflation is $8\mathrm{.}7\%$ compounded annually, how much should the man deposit now?