Answer
(a) $9.042\times 10^{-3}rad$
(b) $2.1m$
Work Step by Step
(a) We can find the angular size of the Moon as follows:
$\theta=tan^{-1}\frac{y}{x}$
We plug in the known values to obtain:
$\theta=tan^{-1}\frac{3476}{384,400}$
$\theta=9.042\times 10^{-3}rad$
(b) We know that
$tan\theta=\frac{d}{x}$
This can be rearranged as:
$x=\frac{d}{\theta}$
We plug in the known values to obtain:
$x=\frac{0.019}{tan(9.042\times 10^{-3})}$
$x=2.1m$
