Since, they have synchronous counters, same clock frequency will reach to every FFs. So, basically 80 kHz will be sent to D2, and the frequency will reduce by half at output f1. So, f1 = 80/2 = 40kHz. Similarly, f2 = 40/2 = 20 kHz.
So, f1/f2 = 40/20 = 2
