Answer
Option 2
The part of the job that Marina can complete in 1 hour
Explanation
Working together, Katherine and Marina can sand a large cabinet in 2 hours.
In hour the complete 1/2 of total work
It would take Katherine 10 hours to do the job alone.
In one hour Katherine complete 1/10 of total work
Let r, the part of the job that Marina can complete in 1 hour
So we can write,
r = 1/2 -1/10 = 0.4
The part of the job that Marina can complete in 1 hour is 0.4
