I have tried this problem numerous times and cannot solve for the variance. Can someone help me?

"In a game a player either wins $10 with a probability of 1/8 or loses $1 with a probability of 7/8. What are the expectation and variance of the total net winnings of a player after 50 turns at the game?"

I found the expectation to be 18.75 dollars, but cannot get the variance which is supposed to be 25.72 dollars. Is the book wrong or is it just me?

Thanks