Two sisters, Allie and Bonnie are saving money for a trip to Europe. Allie has $1500 and adds $500 each month to this amount. Bonnie has $2300 and adds $400 each month to this amount. How many months must Allie save to exceed the amount of money that Bonnie has saved?
A) 6 months
B) 7 months
C) 8 months
D) 9 months