Question 767291
let  airplane can take to complete the task  x hrs 
and other   can take y hrs
first plane  hrs work=1/x
second plane 1 hrs work =1/y
both plane 1 hrs work =1/x +1/y
both plane 3hrs work =3/x+3/y and work completed 3/5
remaining work =1-3/5=2/5second has to finished the work in 9/2 hrs
full work can be done by second plane  in 9/2x2/5=45 hrs
full work can be done by first alone = 45/8 hrs