Work Problem

Lindsay can paint 1/x of a certain room in 20 minutes. What fraction of the same room can Joseph paint in 20 minutes if the two of them can paint the room in an hour, working together at their respective rates?

A. 1/3x
B. 3x/x – 3
C. x – 3/3x
D. x/x – 3
E. x – 3/x

Lindsay ---- 1/x room in 20 min or whole room in 20x min
or 1/20x room in 1 min

Lindsay + Joseph ---- 1 room ---- 60 min
or 1/60 room in 1 min

So Joseph in 1 min = 1/60 - 1/20x = (x - 3)/60x
So Joseph in 20 min = 20(x-3)/60x = x-3/3x

Thanks really appreciate it