Final answer:
The correct usage of numbers in the given sentence is "Sean is leaving work at 4 o'clock today to go to a doctor's appointment." It is standard to use numerals followed by "o'clock" for expressing time without additional letters or hyphens.
Step-by-step explanation:
The sentence that uses numbers correctly is: Sean is leaving work at 4 o'clock today to go to a doctor's appointment. When expressing time in writing, numerals are often used followed by "o'clock" without additional designations such as 'o' or hyphens. The exception is when writing dialogue or more formal writing, where you might spell out the time.
Other examples of using time correctly include saying "They're leaving for the airport at 10:30." This contraction joins 'they' and 'are'.
When calculating elapsed time, as in the scenario with Maria running errands, we add the duration of each activity to determine the end time. Maria's total time spent would include the sum of minutes at each errand and the drive time.