Suppose you toss a coin and will win $3 if it comes up heads. If it comes up tails, you toss again. This time you will receive $6 if it comes up heads. If it comes up tails, toss again. This time you...

Suppose you toss a coin and will win $3 if it comes up heads. If it comes up tails, you toss again. This time you will receive $6 if it comes up heads. If it comes up tails, toss again. This time you will receive $12 if it is heads and nothing if it comes up tails. What is the mathematical expectation for this game?