Geography: Finding difference in longitude?

Question

I need more help in trying to figure out how to find longitude. It's very confusing for me, so a detailed explanation would be greatly appreciated! Thanks!

How many degrees of longitude lie between 168 East and 177 West (the shortest distance)?

Answer 1

there are 180 E longitudes and 180 W longitudes.

the least number= (180-168)+(180-177)

                            =12+3

=15

for finding the least number of longitudes

1) find the sum of the longitudes

in this case =168+177=345

2)find the sum of 180-(the given longitude) for each case

in this case 180-177+180-168

=15

which of tje 2 cases gives the least answer will be the answer