The one I'm having trouble with is, $\displaystyle tan \theta \frac{4}{3}, \theta$ in quadrant $\displaystyle III$

I've solved $\displaystyle y=\sqrt{3},x=-1,$ and $\displaystyle r=2$

My problem is I can't put $\displaystyle \frac {\sqrt 3}{4}$ in to my calculator. I've tried $\displaystyle \frac {1.7321}{2}$, but I can't do decimals as fractions.