Question 288393
Brother got a 10 minute head start
In those ten minutes he went 9*1/6=9/6=1.5 miles
We are gaining on him at 3 mph.
So it will take 30 minutes to catch up

another way to do this 
9*(x+1/6)=12*x
9x+1.5=12x
1.5=3x
1.5/3=x
1/2=x
x= 1/2 hr.