Originally Posted by
skeeter $2\left(-\dfrac{2k}{b^2}+2b\right) = 0 \implies 4\left(-\dfrac{k}{b^2}+b\right) = 0 \implies \color{red}{b = \dfrac{k}{b^2}}$
... this is the value of $b$ that minimizes the volume.
Oh yes of course, thanks.
from the original equation for volume ...
$k = b^2 h \implies \color{red}{h = \dfrac{k}{b^2}}$
take a look again at your first post ... what you were supposed to show?