Question: Can you give me some step-by-step instructions for this math problem: John invited 20 people to a birthday party.  Each guest will eat 2 hot dogs.  He already has 4 hot dogs left over from a previous party.  If a pack of hot dogs contains 6 hot dogs and costs $2, how much does he need to spend on hot dogs?
Answer: 
He needs 2*20=40 hot dogs
So he needs another 40-4=36 hot dogs
So he needs to buy 36/6=6 packs of hotdogs
That means he needs to spend 6*2=$12