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**Black** Given is

$\displaystyle \frac{dh}{dt}=20 \times 10^{-2} \, \text{m/min}$.

Your objective is to find

$\displaystyle \left. \frac{dV}{dt}\right|_{h=1.5}$

Volume of a cone w/ radius r and height h is

$\displaystyle V=\frac{1}{3}\pi r^2 h$.

You want to put V in terms of h alone and differentiate w/ respect to t. Using similarity of triangles you get the equation

$\displaystyle \frac{r}{h}=\frac{1}{3}$.

Solve for r, plug it in the volume equation, then differentiate w/ respect to t.