Every 15 degrees along the line of longitude is equivalent to a time difference of 1 hour.
Given that it is 10:00 am at your location when it is noon along the prime meridian, this means that you are 2 hours behind the prime meridian.
The prime meridian is 0 degrees and you are 2 x 15 = 30 degrees west of the prime meridian.
Therefore, your longitude is 30 degrees west.
