What is a little bit of money for a small family - but still a living wage - is going to be a bit more for an individual. Some countries make up the difference by giving parents of children some money each month.
So that the employers do not have to take the family situation of the people they employ into account.
Np. As for the $2400, $15/hour * 40 * 4 is close enough, and that seems to work based on the salaries of a number of people that I am familiar with.
Working two jobs at $7/hour should not be a requirement to make ends meet. And that's another way in which the low minimum wage hurts employment: people working two shifts because they have to.
What is it, then? Small family or individual?
(Edit: sorry for the annoyance. I just tried to understand how did you work out that the right number is $2400 with such precision. Surely that's the right number everywhere in the US, as well...)