The Prime Meridian itself is defined as zero longitude. There is no such thing as
the number "closest" to zero. Whatever number you mention, no matter how
small it is, I can always come up with a number that's smaller than yours ...
closer to zero ... but not there yet.
On the equator, 0.000000229 degree (0.000824 second) west longitude is one inch
west of the Prime Meridian. But you can fit a lot of other, smaller, numbers inside
that one inch.
The question is a lot like asking "What's the smallest amount of water that a glass
can hold ?", or "What's the length of the shortest line you can draw on paper ?"
Without getting into molecular physics or quantum cosmology, there are no such things.
"240 degrees east of the Prime Meridian" places you at 120 degrees west longitude.
The Prime Meridian is defined as zero longitude. All longitudes on Earth are measured east and west from there.
At zero degrees longitude. Only on one side, the other side is the international date line.
The Prime Meridian is a line of longitude stretching from the North Pole to the South Pole. It goes through the continents of Europe, Africa, and Antarctica.
The Prime Meridian is longitude 00 and runs north-south through Greenwich (London.)Its counterpart is longitude 1800 that runs over the Pacific Ocean. They meet at the North and South Poles.
The prime meridian is a line of longitude. Nothing can be closer to something than itself.
Zero.
The Prime Meridian itself is defined as zero longitude. (0°) You can't get any closer to it than that. The higher the number of degrees of longitude, the farther a given longitude is from the prime meridian. The maximum is 180° either east or west. There is no minimum. Whatever longitude you name, no matter how close it is to the Prime Meridian, I can always name one that's closer to it than yours is. It's like asking "What is the smallest number ?" There's no such thing.
Lines of longitude run north-south from pole to pole. They are an angular measure of how far east or west you are of the prime meridean which runs, north-south, through Greenwich, England.
Vertical
Yes it does.
Lime, Peru is 77.1 degrees of longitude from the Prime Meridian, and about 5,005 miles from the closest point on it. Philadelphia, PA is 75.2 degrees of longitude from the Prime Meridian, and about 3,304 miles from the closest point on it. Philadelphia wins both measurements.