Jaces dad drives 605 miles in 11 hours

I'm not sure what the question is but, I'm guessing you are trying to find out how many miles are driven per hour. 

To determine how many miles are driven per hour, you would divide the total number of miles driven by the total number of hours it took to drive it. 
605 ÷ 11 = 55mph

Jace's dad drove 55 miles per hour. 

I hope this helps!

8,400-6,400=xx/6,400anyways the percent increase is 31.25% or 0.3125 you can round if you can