All you need is the population of LA and Memphis. The population of Oakland was extra info
LA:
Memphis:
642,000
You then divide 6 by LA and see if it is roughly the same as Memphis:
3,810,000 / 6 = 635,000
Is it around the same?
YES! They are only a couple 10,000 off! This means the answer is true!
Hope this helped! Let me know if there is anything I need to clarify or explain more in depth!