Question 893074
More than one way to do this.


RATES:
Carpenter, (3/2)r
Helper,  r
Carpenter&Helper, 1/15
Unit is jobs per day.


Combined rate is their sum.

{{{highlight_green((3/2)r+r=1/15)}}}
Solve for r and find its reciprocal; and this is how many days the helper needs to do 1 job.