Driving along a crowded freeway, you notice that it takes a time t to go from one mile marker to the next. When you increase your speed by 8.4 mi/hr, the time to go one mile decreases by 14 seconds. What was your original speed? (rounded to the nearest whole number).

distance = rate * time

Therefore, time = distance/rate.

Time before speeding up was t. Time after speeding up was 14 seconds faster.

Rate before speeding up was r. Rate after was 8.4 mph faster.

Time_after = Time_before - 14

distance/rate_after = distance/rate_before - 14

1/r = 1/(r+8.4) - 14

Can you solve for r now?