Value of an existing forward

On some date in October an investor entered an OTC long forward on the Nifty 50 for 29 Dec 2026 delivery at $K = 24{,}200$ (hypothetical). On 5 Nov 2026 ($T = 54/365$): (a) Value the forward per index unit and for 65 units using $r = 5.50\%$, $q = 1.42\%$. (b) Value it instead using the market Dec futures price as the forward price, discounting at 5.50%. Explain the difference between (a) and (b). (c) Show that $\partial f/\partial S = e^{-q\tau}$ and interpret.