The time t required to drive a certain distance varies inversely with the speed r. if it takes 4 hours to drive the distance at 35 miles per hour, how long will it take to drive the same distance at 45 miles per hour?

The formula for this is t = k/r, read "t varies inversely as r". If the info they give us is 4 hours and 35 miles per hour, we find that k = 140. Now use that 140 in another equation to solve for t: t = 140/45, and t = 3.1 hours