Answer
$17km$
Work Step by Step
S=1.7m
wavelength = $650nm$
$D=7\times10^{-3}m$
So, $\theta_{min}=\frac{1.22\times wavelength}{D}=9.58\times10^{-5} rad$
$S=r\theta_{min}$
Thus, $r=\frac{S}{\theta_{min}}=\frac{1.7}{9.58\times10^{-5}}=17.7km$
So the distance between the car and the observer can be taken as 17 km (maximum).