If the equal is 55x + 35y = 200
x: time-driven at 55 miles/hour
y: time-driven at 35 miles/hour
If the car spends 2.5 hours at 35 miles per hour, then it drove:
55x + 35(2.5) = 200
55x =35
y = 112.5
There the drive spent about 2.5-hour driving at 55 mph.
Hope it helps!
