I’m terrible at arithmetic, but one very useful skill I have (probably left over from my slide rule days) is doing 1 1/2 digit calculations with exponential not

I’m terrible at arithmetic, but one very useful skill I have (probably left over from my slide rule days) is doing 1 1/2 digit calculations with exponential notation in my head. Like your evaporation problem. These days, though, I have a tendency to just raise my wrist and ask Siri, “How many inches to the Sun?”