Total distance John drove=450 miles
total time=8 hours
let the number of hours he drove on highway be x, number of hours he drove on turnpike will be (8-x) hours
since
distance=speed*time
distance traveled in highway=50x
distance traveled in turnpike=60(8-x)
thus the total distance will be:
50x+60(8-x)=450
simplifying the above
50x+480-60x=450
-10x=450-480
-10x=-30
thus
x=3 hours
Thus he drove on highway for 3 hours.
