Answer:
3 hours 15mins
Step-by-step explanation:
in 1 hours time, A will complete 1/15 of the job, B will complete 1/18 and C 1/15.
After 3 hours, A completed 3/15 (aka 1/5) of the job, B 3/18 (aka 1/6) and C being the same as A.
total job done after 3 hrs is 1/5 + 1/6 + 1/5 which is 17/30 of the job
left: 13/30
in 1 hr, A and C will do 2/15 of the job (4/30)
therefore, no. of hours needed: 13/4 hours = 3.25 hours (3 hours 15mins)
