Need formula help

The area of a circular sector with radius $r$ and angle $\theta$ (in radians) is
\[A=\frac{r^2 \theta}{2}.\]
In the given exaample we have $r=12$ and $A=75$. Substituting in the above formula we get
\[75=\frac{12^2 \theta}{2}=\frac{144 \theta}{2}=72\theta.\]
Hence
\[\theta =\frac{75}{72}   \text{radians}.\] 
If you want the angle in degrees then it is 
\[\frac{75}{72} \times \frac{180}{\pi}=60.523    \text{degrees}.\]