Raven has been babysitting to earn enough money to buy a concert ticket that costs $24. She already had $12 and she earned $20 babysitting. Which expression represents how much money Raven has left after she buys the concert ticket?
A) 12 – 20 – 24
B) 12 + 20 – 24
C) 24 – 12 + 20
D) 24 – 12 – 20