A roulette wheel has 38 slots, 18 of which are black, 18 are red, and 2 are green. Each time the roulette wheel is spun, the roulette ball is equally-likely to fall into any of the 38 slots. If a player wagers, say, $10 on red and wins, then the house returns her $10 wager along with another $10. If the player loses, the house keeps her wager. If a player wagers $10 on red, what is her expected gain?