53.5°
Sine and cosine of complementary angles. Thus,
[tex](\frac{x}{2} + 20 ) + (2x - \frac{25}{2}) = 90[/tex]
[tex]x = 33[/tex]
then,
[tex]\frac{33}{2} + 20[/tex] → [tex]x= 36.5[/tex]
[tex]2(33) - \frac{25}{2}[/tex] → [tex]x = 53.5[/tex]
thus,
β [tex]= 53.5[/tex]