Answer:
f - f '= 6.18*10^11 Hz
Step-by-step explanation:
The change in frequency is given by:

f': observed frequency
f: source frequency = 6.17*10^14 Hz
v: speed of the source = 3.01*10^55 m/s
c: speed of light = 3*10^8 m/s
By replacing all these values you obtain:

hence, the change in frequency f-f' will be:
f - f '= 6.18*10^11 Hz