The closest Idaho ever gets to 100 degrees west longitude is along its eastern border with Wyoming, at about 111 degrees west.
The center of Boise, Idaho is at about 116.2 degrees west longitude.
The degree of longitude equivalent to east of 5 degrees west longitude is 355 degrees. This is because there are 360 degrees in a full circle, so moving 5 degrees east from 5 degrees west would place you at 355 degrees longitude.
The capital of Idaho is at Boise. The longitude of Boise is roughly 116.19° West. That's 16.19 degrees west of the 100° W meridian. (But you could also reach Boise by traveling 343.81 degrees east from the 100° W meridian.)
East
To convert decimal degrees east to decimal degrees west, you can subtract the east longitude from 360. For example, if the longitude is 80 degrees east, to convert it to degrees west, you would do: 360 - 80 = 280 degrees west.
23 degrees east
180 degrees east/west longitude
Coordinates given in WikiPedia indicate a longitude of 21 degrees east. This puts the point at which this coordinate is set east of the 20 degree line.
One gains a day and from east to west one looses a day.
Sheikh Zayed City, west of Cairo.
The state capital that is east of the 90 degree west longitude line is Jackson, Mississippi. It is located in Hinds County in the northeastern part of the state.