Answer
$L = 55~km$
Work Step by Step
We can write an equation for the resolution:
$\theta_{min} = \frac{1.22~\lambda}{D}$
$\theta_{min} = \frac{(1.22)~(600\times 10^{-9}~m)}{0.040~m}$
$\theta_{min} = 1.83\times 10^{-5}~rad$
We can find the distance $L$:
$\theta = \frac{d}{L}$
$L = \frac{d}{\theta}$
$L = \frac{1.0~m}{1.83\times 10^{-5}~rad}$
$L = 5.5\times 10^4~m$
$L = 55~km$
