Next, the minimum wage in constant 2012 dollars was $10.50/hr in 1968. In 2012 it is $7.25 (isn't it?).
Now here is the part that is going to be difficult for you, so please pay close attention. If the productivity of the 1968 worker is the same as the 2012 worker, how much do we have to raise the 2012 minimum wage by in order to bring it into exactly the same relation to productivity as existed in 1968. (I know it's difficult, but I also know you are smart enough to do it.) OK did you do it? The answer is below if you're having trouble. Don't peek!
Now I am not inclined to look up the real cost of labor (defined however you like as long as you use a consistent definition, e.g, poverty level for a single person) in 1968 versus 2012, but I'll give you a hint. It is very likely going to come out somewhere between 10 and 11$ per hour, or more in 2012. And in 1968 it is going to come out at between 1 and 2$ per hour, or more. At $1.75/hr (the minimum wage in 1968) it would be $10.50/hr in 2012 dollars.
The final step, and you're completely on your own here, because to get good at this stuff you have to practice. Compare the real cost of minimum wage labor in 1968 to the real cost in 2012. Take the difference between those real costs and the actual hourly wages in nominal dollars in 1968 and 2012. Which year has the biggest gap between hourly wage and real labor cost. Then as I suggested, look up the size of the welfare roles in those two years per capita, and see if you can come up with a reasonable hypothesis for how the gap between real labor cost and the minimum wage is made up. I know that is a lot to ask, but that's all the help you're going to get from me young man.
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answer: $3.25/hr. (I hope you didn't have to peek!)
P.S. You might want to know what some arbitrary cost of living equivalent to what we call a "living wage", or say the poverty level, has to do with the real cost of labor. Well, consider if you can hire a worker who can not afford clean clothes, basic dental and healthcare, a shower, transportation to work, a good night's sleep, and enough to eat to keep from starving. There is obviously, then, some minimum cost associated with the minimum wage worker, regardless of whether you pay it all or someone else pays part of it. That minimum cost is the real cost of labor.