Step-by-step explanation:
the expected value is calculated by multiplying each of the possible outcomes by their probability, and then summing up all these results.
tossing a coin 2 times gives us 4 possible different outcomes (all with the same probability of 0.25) :
head - tail
head - head
tail - head
tail - tail
to have exactly one head is 2 out of these 4 possible outcomes, and the probability is 0.5.
everything else is also 2 out of these 4 possible outcomes, and the probability for that is therefore 0.5 too.
the expected value (from your point of view) is
9×0.5 - 15×0.5 = -$3.00
