What bolt pattern

I have a 74 Dart Swinger originally a 318. It has 15x7 police wheels on it now. Not sure bolt pattern.
I searched bolt pattern trying to figure out how to measure to see what bolt pattern I have. I got a bunch of results but not what I was looking for. Can someone post a diagram or pic of how to measure.
I drive my car everyday and really should have a spare in the trunk.
Thanks