12 coins are tossed and placed in a line. each coin can either show a head or a tail

Ok, so each coin has two possibilities. Heads or Tails. And since there are a total of 12 coins, each possibility can only show up 12 times. This is represented by 2^12. 12 times two different options can show up. That's what I think.

Coins can either be heads or tails. For each coin there are two possibilities. Your answer is 2^12.