If the propeller rpm is fixed and the airspeed increase, the angle of attack of the blade:
As worded, this is a very tricky question. If the RPM is fixed, that's a very different thing to a fixed pitch prop, and the answer to the question will be different.
If the RPM is fixed, that is either (in the case of a fixed pitch prop), because the pilot is adjusting the throttle to maintain the RPM constant with an airspeed change, or the prop is operating normally as a governed constant speed prop to maintain the same RPM with power and airspeed changes.
So in the case of a fixed pitch prop, whose RPM is fixed [by pilot action] as airspeed increases, the pilot must be closing the throttle as the airspeed increases (and developing less power) to remove the engine power which would normally increase engine speed as the airspeed increases - in a descent, I presume.
Therefore there are more variables affecting blade AoA than just RPM and airspeed, there is also the power being transmitted into the air (reducing), and power required for level flight (also reducing).
So think this tricky question through really carefully.....