Quick way on the Bus/737 is to use the METERS (or METRES) button.
At 30,000ft, select METERS. It will show approx 9,100m. Take the first two numbers - 91.
You need 91nm plus some extra miles for speed reduction plus or minus some miles for tail/headwind.
I always round it up for sake so 100nm from FL300.
During descent, I am checking distance on progress page against my altitude using the METERS button.