Final answer:
To calculate the latest time Larry can start his tour to make it to dinner by 7:45 P.M., subtract the total tour time from 19:45 (converted from 7:45 P.M.).
Step-by-step explanation:
To calculate the latest time Larry can start his tour to make it to dinner by 7:45 P.M., we need to determine the total time he will spend at the three locations. Let's say Larry spends x hours at the first location, y hours at the second location, and z hours at the third location. The total time Larry will spend on his tour is x + y + z hours.
Since Larry wants to make it to dinner by 7:45 P.M., we need to subtract the total tour time from the dinner time. Convert 7:45 P.M. to 24-hour format, which is 19:45. Subtracting the total tour time from 19:45 will give us the latest start time for Larry's tour.
Latest Start Time = 19:45 - (x + y + z) hours