What line measure distances east and west of the prime meridian?
Longitude is the measure of distances East and West of the Prime Meridian which runs through Greenwich, England
What lines run north and south through the poles and measure distance east or west of the prime meridian?
The longitude line measures the angle east or west of the prime meridian. If you want the actual distance you'd travel directly east or west until you hit the prime meridian, you must multiply this angle (converted to radians) by the radius of the earth, and then multiply by the cosine of the latitude angle, which gives the angle north or south of the equator.
Longitude is the angular measurement in degrees east or west of the Prime Meridian. The Prime Meridian is at zero degrees; going east, your longitude is in degrees and minutes east, while going west your longitude is measured in degrees and minutes west. A circle is 360 degrees, so the maximum longitude is 180 degrees either way. At the 180 degree line (called the "anti-meridian") the measurement is neither east nor west.