Help Calculating Angle $\alpha$ in Sketch

[DanielBW]

Hello everyone! I need your help with the next sketch:

View attachment 3638

I need to find the angle between the red line and the horizontal ($\alpha$). I did try everything that i could imagine but even so i couldn't find it.

According to the book, the angle should be: $\alpha=20~degrees$

How can i calculate it?

 

[Ackbach]

I think your picture here is cut off, and you're missing too many dimensions in the drawing for us to be able to help you out here. Could you please rescan with more of the drawing in the picture?