The machine could punch out 500 plastic pterodactyls in 20 minutes at that rate how many could it punch out in 1 and 1/2 hours

I would find it easiest to reduce the number to minutes, like this: 500 in 20 minutes would be 500 divided by 20 = 25 pteradactyls / min.

There are 90 minutes in an hour and a half, so 25 x 90 = 2,250 pteradactyls in 1 1/2 hours.