Hello from MrBillDoesMath!
Answer: 28.61 degrees
Discussion:
While the triangle appears to be upside you can't fool the tangent function! In this triangle,
tan (b) = opposite /adjacent ( where "b" means beta)
= 6 /11 ( it's a 6 not a 9, I believe !)
so "b" = inverse tangent of ( 6/11) or approx 28.6104 degrees.
To my mind there is a bit of confusion as to whether 6 or 9 was intended for the side opposite the angle. This point needs to clarified and the diagram updated appropriately.
Thank you,
MrB