One night 18 percent of the female officers on a police force were on duty. If 144 police officers were on duty that night and half of these were female officers, how many female officers were on the police force?	Select.
A) 300
B) 400
C) 500
D) 600
E) 700

Rationale: "let x be the number of female police officers on the police force . the number of female police officers on duty was 72 . 0.18 x = 72 x = 400 the answer is b ."
Answer: B