B. 24,000.
The car was worth 24,000 when she bought it.
25% = equivalent of the decreased value
18,000 = net of the decrease value
Original value = 18,000 / (100% - 25%)
= 18,000 / 75%
Original value = 24,000
Decrease value = 24000 * 25%
= 6000
Net Value = 24,000 - 6000
= 18,000