Question 906390
x/a+x/b=1
.5/10+x/10+x/14=1
3.5/70+7x/70+5x/70=1

12x/70=66.5/70
12x=66.5
x=66.5/12
x=5 6.5/12
or 
x=5.5417 hrs
5 hr 32 minutes 30.12 seconds

if they had started together it would be x=5.83 hours