12:45 pm to 6:15 pm is 5 hours 30 minutes. So you start out with $1.50 for the first hour and $0.55 for additional half hour. So altogether you have 11 half hours. So you would take $0.55 times 11 which gives you $6.05. Then add 6.05 and 1.50 which gives you 7.55. So your answer is $7.55
