What is the length of the line segment rounded to the nearest tenth of a centimeter?

Marcus worked 8 hours on Monday without taking a break. He had a meeting that lasted h hours and divided the remaining time equally over 4 tasks. Which expression gives the amount of time he spent on one of the tasks?

The mass of the Earth is about 5,973,600,000,000,000,000,000,000 kg. The mass of Venus is about 4,867,000,000,000,000,000,000,000 kg. What is the difference of their masses in scientific notation?