The airport is 2,000' above the 1003 hPa QNH Pressure Datum.
This is 10 hPa
above the 1013 hPa Pressure Level, which places the
QNH Datum 10 hPa x 30' = 300' above the 1013 Pressure
Level.
Therefore, the airport is 2,000' + 300'
= 2,300' above the Pressure Level, i.e. FL 023.
The aircraft climbs from FL 023 to FL
050 = 2,700'.
At a rate of 500' fpm, this equals
2,700 / 500 = 5.4 minutes (0.09 hours)
Groundspeed = 100 KTAS - 20 kts Headwind = 80 kts
On CRP 5:
Place 1:60 Index on Inner Scale against
80 kts GS on Outer Scale
Read 5.4 minutes on Inner Scale against
7.2 NM on Outer Scale
Mathematically:
Distance = Speed x Time
Distance = 80 kts x 0.09 hours
Distance = 7.2 NM