What is the method for calculating the angle Θu in compressible flow?

[pipe08]

Hello good people!

I'm studying the compressible flow and the book refers to this example. I can't understand how does it calculate the angle Θ_u?
In the previous example, there is a method to calculate it but it requires all the properties once the fluid is deflected, therefore, that's not the way because they are asking for the pressures.

anything light is greatly appreciated.

 

[boneh3ad]

Much like $\theta_l$, $\theta_u$ is set by the surface inclination due to the no-penetration condition.