You can put this solution on YOUR website!
I really admire the fact that you considered whether your answer made sense or not. At first glance, it doesn't seem logical to me either, but wait...
Consider how long it would take Eva to paint the 4 rooms by herself. Since she does 3 rooms in 7 hours, she paints 1 room in
hour. Therefore she should be able to paint 4 rooms in
But Eva and Anna together take 9 hours to paint the 4 rooms. That means that Anna's contribution to the work is very small, i.e. she only reduced the elapsed time by 20 minutes. That tells me that Anna works VERY slowly, so 63 hours per room or 126 hours for 2 rooms is not an unreasonable result after all.
What might be considered illogical is if Anna keeps her job as a painter. Myself, I'd fire her and hire another Eva.