On monday, roger drove to work in 20 minutes. on tuesday, he averaged 15 miles per hour more, and it took him 6 minutes less to get to work. how far in miles does he travel to work?

Let the distance to his office be x, then

On monday, speed = x/20 miles per minutes = 3x miles per hour

On tuesday, speed = (3x + 15) miles per hour

Time = distance / speed

(20 - 6) / 60 hours = x / (3x + 15) hours

7/30 = x / (3x + 15)

7 (3x + 15) = 30x

21x + 105 = 30x

30x - 21x = 105

9x = 105

x = 105/9 = 11.7 miles

Therfore he travels an average of 11.7 miles to work.