The teacher per-hour pay thing is a raging controversy. There are a lot of things that aren't clear about how you should measure: should teaching be considered a 12-month job or 9? (It prevents you from taking equally remunerative, professional jobs over the summer (so you need to be able to live on it as a 12-month salary) and you need to put in time over the summer to do the job well, but you're really only at work for 9 months and that's all some people do.) Should only contracted hours or overtime count? (Many teachers, especially new-ish teachers, put in time beyond their contracted hours, but some argue that many professional jobs require this and, eg, lawyers don't go whining about it. (I'm dismissive, in that salaried jobs requiring substantial overtime are, by and large, more prestigious and remunerative than teaching by a fair sight.))

So, yeah, it's very unclear which hours you count. I think you'd also find that the distribution of hours worked is enormous, which means any single number you come up with will be just wrong. (For example, were you to look at only first-year teachers -- who, coincidentally, have the lowest salaries -- I expect you'd find 60-80 hours/week is common. As time goes on, I suspect you'd find a lower average but a much wider range.)