Question 821197
in three days Jon completed 3/15=1/5 of the job.
3/15+x/15+x/45=1
3x/45+x/45=12/15
4x/45=4/5
x/9=1
x=9 they worked 9 days together

check
3/15+9/15+9/45=1
3/15+9/15+3/15=1
15/15=1
ok