suppose Jane can finish cleaning by herself in x minutes, every minute she does 1/x portion of the work
Anna can finish cleaning by herself in 2x minutes, every minute she finishes 1/(2x) portion of the work
together, they finish (1/x +1/2x) portion of the work
in 15 minutes, they finish the whole work: 15/x +15/2x =1
solve for x: 30/2x +15/2x =1. x=22.5
2x=45
Anna can finish cleaning by herself in 45 minutes.
