Statstics. Can you show me by steps?

Question

In the American version of the Game Roulette, a wheel has 18m black slots, 8 red slots and 2 green slots.  all slots are the same. a person can wager on either red or black. green is reversed for the house. If a player wagers 5$ on either red or black and that color comes up they win 10$ other wise they lose their wager. What is the expected value of playing the game once?

Answer 1

Despite what you may have read or seen before (a wrong answer has been posted all over the internet), the correct answer is -.26