70nm at original ground
speed (180kts) would take 23.3 minutes.
Aircraft has covered 70nm
in 20.3 minutes = ground speed 207kts.
Remaining distance to run
is 320 – 70 = 250nm and at revised ground speed of 207kts this will take 72.5
minutes.
Total elapsed time = 20.3
+ 72.5 = 92.8 minutes (1h33m).
Departure time is 1200
add elapsed time 1h33m, ETA = 1333.