Sydni spent the first 120 miles of her road trip in traffic. When the traffic cleared, she was able to drive twice as fast for the remaining 300 miles. If the total trip took 9 hours, then how fast was she moving in traffic?
Let Sydni's speed in heavy traffic = S
Her speed on 300-mile highway =2S
120 / S + 300 / (2S) = 9 hours, solve for S
S = 30 mph - her speed in heavy traffic.