Answer:
about 48.62 mph
Step-by-step explanation:
You want Kevin's speed while it was snowing if he drove 50 miles at that speed, then 30 more miles at a speed 15 mph faster. His total travel time was 1.5 hours.
The relationship between time, speed and distance is ...
t = d/s
If we let s represent Kevin's speed when it was snowing, then s+15 was his speed when it stopped. His total travel time is the sum of the times at the two speeds:
1.5 = 50/s + 30/(s +15)
Multiplying by 2s(s+15), we get the quadratic equation ...
3s² +45s = 100(s +15) +60s
3s² -115s = 1500 . . . . . subtract 160s
3(s -115/6)² = 1500 +3(115/6)²
s -115/6 = √(31225/36) = (5/6)√1249
s = (5/6)(23+√1249) ≈ 48.62 . . . . . . miles per hour
Kevin's speed while it snowed was about 48.62 mph.