Which one is it?

Can someone answer these problems for me

The physical fitness of an athlete is often measured by how much oxygen the athlete takes in (which is recorded in milliliters per kilogram, ml/kg). the mean maximum oxygen uptake for elite athletes has been found to be 60 with a standard deviation of 7.2. assume that the distribution is approximately normal.

If 10 men take 18 days to mow 60 acres of grass, how long will 15 men take to mow 80 acres?