To determine the amount of potato peeled in 12 hours:
Sam takes 4 hours to peel 32 potatoes
Sam take 1 hour to peel 32 / 4 potato
Josh takes 5 hours to peel 30 potatoes
Josh takes 1 hour to peel 30 / 5 potato
Sam peels 8 potato
They will peel hepotatoeel together in 12 hours