Question 272217
Let x=amount of time it takes B to clean the garage
Then x/2=amount of time it takes A to clean the garage

B works at the rate of 1/x of the garage per hour
A works at the rate of 1/(x/2) or 2/x of the garage per hour
Together they clean at the rate of 1/x + 2/x of the garage per hour
But we are told that together they can clean the garage in 3 hours, so together they work at the rate of 1/3 of the garage per hour, so our equation to solve is:
1/x+2/x=1/3 
3/x=1/3 multiply each term by 3x
9=x
x=9 hours ----amount of time it takes B to clean the garage
x/2=9/2=4.5 hours------amount of time it takes A to clean the garage

CK
In 3 hours, B cleans (1/9)(3)=3/9 of the garage
In 3 hours, A cleans (2/9)(3)=6/9 of the garage
And 3/9+6/9=9/9 or 1 garage

Hope this helps---ptaylor