Welcome to SolidWorks forums Anahita.
You've added/uploaded thae part files along with the assembly so it is not easy to open the assembly file. Well what I did was started a new sketch and insert the picture into that using Tools > Sketch Tools > Sketch Picture. Now I drew two lines on the angle and measured the angle between them which is approax 59.3° (might be 60°).
If you've the part files available then go to configuration tab and there should be a configuration for the alternate position view.
You might also find this post helpful for your future reference.
Alt Postion Config.PNG 10.8 KB