$₹ 17{,}500$
$₹ 18{,}000$
$₹ 16{,}000$
$₹ 16{,}500$
Step 1: Use capital--time (money $\times$ months).
Rahul: $8000\times 12=96000$ money-months.
Sanjay: Let capital $=S$, time $=6$ months $\Rightarrow$ $S\times 6$ money-months.
Step 2: Equal profits $\Rightarrow$ equal capital--time.
$S\times 6=96000 \Rightarrow S=\dfrac{96000}{6}=16000$.
$\Rightarrow\ \boxed{₹ 16{,}000}.$