For a Kaplan (axial flow) turbine, the outlet blade velocity diagram at a section is shown in figure.

The diameter at this section is 3 m. The hub and tip diameters of the blade are 2 m and 4 m, respectively. The water volume flow rate is 100 m³/s. The rotational speed of the turbine is 300 rpm. The blade outlet angle β is _________ degrees (round off to one decimal place).