Question 520542
Rosita can do 1/60 job in 1 min. 
d=minutes it takes Debbie to do the job. Debbie can do 1/d the job in 1 min.
Together they can do 1/15 the job in 1 min.
1/60 + 1/d = 1/15
d+60=4d Multiply by 60d.
3d=60
d=20 min
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Ed