A pie takes 2/3 of an hour to bake if a pie is put into the oven at 7:30 at what time does it need to be taken out.

You would have to take the pie out at 8:10, because 2/3 of an hour is 40 minutes. To make the addition of time easier break it up into bits, like for here you could say, 7:30 plus 30 minutes out of the 40 is 8:00 then you could just add the extra ten minutes afterwords!
Hope this helps, have a good day!