90 degrees
Halfway between the Prime Meridian and 80 degrees west has to be pretty close to 40 degrees west, we'd say.
90 degrees west longitude
90 degrees west
90 degrees west
90 degrees west
The imaginary line at zero degrees longitude is the Prime Meridian. The imaginary line halfway between the poles is the Equator. The Equator is zero degrees latitude.
90 degrees west
The line 90 degrees west longitude, which includes the cities of New Orleans LA and Memphis TN.
The halfway point between the Prime Meridian (0°) and the 180° line of longitude is the 90° line of longitude, also known as the International Date Line. This line is located in the Pacific Ocean and marks where each new day begins.
latitude
Assuming that "all the way west of the Prime Meridian" would be on the opposite side of the globe from the prime meridian, or at 180o, "halfway west of the Prime Meridian" would be the 90oW meridian.
90° west longitude