From
15:00 to 13:38 = 1hr 22min = 82min (82/60=) 1.367hr
1.
Groundspeed?
GS=Dist/Time
= 570/1.367 = 417kt
2. TAS?
GS 417
and HWC 52kt = TAS 469kt
Now on
the CRP-5 put -48 under mach number index (in Airspeed
window), put TAS (outer scale) and find the reduced mach nr. (inner scale) = 0.80