Related rates problem. Determine the speed of the plane given the following information. 
I started by noting that I am looking for $\displaystyle\frac{dx}{dt}$ and I am given $\displaystyle\frac{d\theta}{dt}=1.5^{\circ}/\mbox{s}$.
I then related $\theta$ to $x$ by $\displaystyle\cot(\theta)=\frac{x}{6000\mbox{m}}$, then taking their derivatives with respect to $t$, I get $\displaystyle\frac{dx}{dt}=-6000\mbox{m}\csc^2(\theta)\frac{d\theta}{dt}$, but i'm not sure if this is correct, this number seems too big, and it is also negative. Thoughts?

you need to use radians, so you need to convert your $\frac{d\, \theta}{dt} = 1.5^\circ = \frac{1.5 \pi}{180}. $ putting that in $$\frac{dx}{dt} = -6000 \csc^2(\pi/3)  \frac{1.5 \pi}{180} = -6000 \times  \frac{4}{3} \times \frac{1.5 \pi}{180} = -209.44\ m/sec $$
