-3 < 12 + 20p < 8

Thanks Melody, I edited the answer using \\\\. Looks better now!

Also, thanks Alan. I changed it from 8/20 to -4/20. 

$$-3 \le 12 + 20p < 8 \\\\ -15 \le 20 p < -4 \\\\ \frac{-15}{20} \le p < \frac{-4}{20} \\\\ \mathbf{\frac{-3}{4} \le p < \frac{-1}{5}.}$$

Aziz,

Thanks for  that great answer, I have given you thumbs up.

I just want to suggest that instead of using right arrows you move to another line, I think it would be easier to read.  You do this in latex with \\   If you want the spacing to be bigger you can use \\\\

This is how I do it because I like my working well spread.  

An error in the upper limit Aziz (you replaced the correct -4 with +8 in the last step!):