Originally Posted by Seat 2A

4. In late 1970 Northwest Airlines operated a total of four daily flights into Anchorage from three different airports in the Continental U.S. Identify each airport and the aircraft type being used on each route.
HINT: All of the aircraft involved had four engines...
HINT: Northwest's Regal Imperial Service would have been offered on two of these routes...

Let's try Chicago and Minneapolis with 747s, and Seattle with a 707-320

Seattle and Chicago are two of the cities, but your choice of aircraft is wrong in each instance. Per the schedule I reference for this question, no 747s were operated to or through Anchorage at this time.

So let's expedite things a bit: Based on what you've correctly provided, let's state what we know and then some...

Chicago to Anchorage: Boeing 707-351
Seattle to Anchorage: Boeing 720B X 2 daily flights
New York City to Anchorage: Boeing 707-351

Well, if not a 707 or 747, SEA-ANC was served by a Boeing 720B ... as for the third NW city in the Lower 48 with nonstop service to ANC, I shall go out on a long limb here and guess JFK with a 707-351

You climbed this tree like an orangutan, J! Spot on!

Originally Posted by Indelaware

The airports are pretty obvious, but the equipment isn't. It is likely that various equipment showed up on the routes in over the late 1970s, but I take a stab at:

MSP DC-10
ORD DC-10
JFK 747

They also, for a time in the late 1970s, operated ANC-SEA. Likely with DC-10s & 727s.