20. (MISC) The original Denver based Frontier Airlines filed for bankruptcy in 1986. The “new” Frontier Airlines – still Denver based – emerged in 1994 and commenced service from Denver to four cities. Identify those four cities.
The "make better sense" comment leads me to believe a couple things ... Frontier reincarnated into smaller cities to the northeast of DEN ... how about these, north to south:- Minot (MOT) Correct!
- Bismarck (BIS) Correct!
- Pierre (PIR) Incorrect
- Rapid City (RAP) Incorrect
You're halfway home,
J 
All of your picks are geographically spot on, so from here it should be pretty easy to clean this up.
31. (1975) Everybody knows about the big three gateway cities for travel from Texas into Mexico, i.e. Dallas, Houston and San Antonio. During the winter of 1975, there was however a fourth Texas gateway. Identify that city as well as the airline and the two Mexican destinations that were served nonstop from it.
Texas International operated between McAllen (MFE) and Mexico City (MEX) for awhile; I'll speculate that the other destination was Guadalajara (GDL)
Texas International is correct. However, although Mexico City enjoyed direct one stop service from MFE, neither it nor Guadalajara enjoyed nonstop service. That's what we're looking for. I apologize for not specifying nonstop. For the record, in
ALL of my questions re. destinations served from one point to another or solely from one airport like this - unless otherwise specified - I'm
always looking for nonstop flights. That said - please, guess again!