Question 29279
I could solve it the longer way, but the shorter way is easier to understand

Chuck shovelled for a total of 30mins {{{20alone+10with Joan}}}
In 30 mins he would have shovelled 30/40= 3/4th of the walk
Joan shovelled for 10mins
She shovelled the remaining 1/4th in 10mins
For her to shovel the entire thing {{{4 * 1/4}}} {{{4*10}}}
So Joan also would take 40mins to shovel the driveway