If $p^3=q^4=r^6=t^7=s^2$, then $\log _t(p q r s)=\ldots \ldots$

The money invested in a company is compounded continuously. If $Rs\, 400$ invested today becomes ₹800 in 6 years, then at the end of 30 years, it will become (in ₹)

If $y=\log _3\left(\log _3 x\right)$ then $\frac{\mathrm{d} y}{\mathrm{~d} x}$ at $x=3$ is $\ldots \ldots$