Plz help!! Roulette Probability?

Can people guide me through this one:"When betting $1 on the number 7 in roulette, there is a probability of 1/38 of winning, and a win results in a net profit of $35. What is the average return for every $1 that is bet?"thanks a million for any help!!

I'm gonna assume that means you add up all the returns and divide by the number of possibilities. So because you lose a dollar usually and gain 35 dollars every 38 times, it would be ((37 * -1) + 35) / 38, or -5 cents. Therefore, don't play roulette. Especially not the Russian kind.