Final answer:
Estimating the sum for tasks that occur in parallel involves using appropriate mathematics to find the longest task duration and using that as a guesstimate for the total time, ensuring the estimate is realistic by performing a sanity check.
Step-by-step explanation:
The best estimate for the sum depends on the context provided by the listed tasks and the approach to estimation being employed. One should utilize appropriate math and sound reasoning to generate a ballpark figure for the sum. Since the tasks are assumed to happen in parallel, the estimate should be based on the longest task duration, as this will govern the overall time frame. The importance of accuracy is highlighted by using one significant figure and performing a sanity check to ensure the estimate is realistic. You might find that the early guesstimates may be either significantly lower or roughly in line with the careful approximation after making proper considerations.