Answer
$360\ m$
Work Step by Step
The height of the mast equals to an arc length subtends to an angle of $\theta=1^\circ45'=(\frac{7}{4})^\circ$. The distance is the radius, we have $11.0=r\theta=(\frac{7}{4})^\circ\times\frac{\pi}{180^\circ}r$ which gives $r\approx360\ m$
