Answer
Please see the work below.
Work Step by Step
We know that the time of flight is
$t=\frac{x}{v}$
$t=\frac{0.001}{12}$
$t=8.333\times 10^{-5}s$
We can find the height as
$h=(\frac{1}{2})gt^2$
We plug in the known values to obtain:
$h=(\frac{1}{2})(9.8)(8.333\times 10^{-5})^2=3.4\times 10^{-8}m$
