Dennis is driving down the East Coast of the United States. He starts in Boston and drives through Hartford, Connecticut, which is approximately 101 miles away from Boston. He continues on from Hartford to Baltimore. a. Write an equation for the length of Dennis’s trip in miles 'D' in terms of the time in hours 't' it takes him to drive from Hartford to Baltimore and the speed he drives in miles per hour 's' while traveling from Hartford to Baltimore.

b. Baltimore is approximately 410 miles away from Boston. Determine Dennis’s average speed from Hartford to Baltimore if that portion of his trip takes 5 hours. Show your work. Justify each step. (You do not need to use "Simplify" as a justification.)