Question 892942
Ryan  finished 4/12 =1/3 of the job in 4 days leaving 2/3 to be done
In two more days Ryan does 2/12=1/6 of the job.
So in 6 days, Ryan has done 6/12=1/2 the job.

Sandra does 1/2 the job in 2 days.
So she could do the whole job in 4 days.

2/12+2/s=2/3
1/6+2/s=4/6
2/s=3/6
2/s=1/2
4/s=1
s=4

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