The parking meter charges $2 per hour, means that each half hour costs $1.
Thus, 1$ pays for half an hour, so d $ pay for d half hours, that is d/2 hours, which is 0.5d hours.
15 minutes a quarter of an hour, which is 0.25 h.
Thus, the driver has a total of d/2 hours that she payed for, + 1/4 hour from the previous driver. These make a total of 3 hours, so we can set the equation:
3=0.5d+0.25
Answer: B