Answer
$d = 50~cot~\theta$
We can graph $d$ on the interval $~~0.6 \leq \theta \leq \frac{\pi}{2}$
Work Step by Step
$d = (h_2-h_1)~cot~\theta$
Let $h_1 = 5$
Let $h_2 = 55$
Then:
$d = (h_2-h_1)~cot~\theta$
$d = (55-5)~cot~\theta$
$d = 50~cot~\theta$
We can graph $d$ on the interval $~~0.6 \leq \theta \leq \frac{\pi}{2}$
