Use distance = rate x time
Let "t" be the time it took for you to drive to your parent's house at 60mph.
So 60t would be the distance.
And "t+40" would be the time it took for you to get to your parent's house at 50 mph. And that total distance would be 50(t+40).
Since both the distances are the same, this gives us the equation:
60t = 50(t+40)
Simplify: 60t = 50t + 2000
10t = 2000
t = 200 minutes
Driving at 60 mph for 200 minutes equates to a total distance of 200 miles.
