Answer:
147 Hz
Step-by-step explanation:
First we need to know what frequency will the waves hitting the whale have respect of it.
The change in frequency is calculated with this equation:

However in this case, the wave is bouncing on the whale and coming back, so there is a double frequency shift (the difference is the same both times because the relative speeds between the two objects is the same both times)

Then:

The frequency shift is positive, it will have increased frequency.