Distance Time word problem

Hi Guys,

I am having trouble figuring out this distance time word problem. I created a table and show my reasoning below but I am getting some weird answers. Can you guys please point out where I am going wrong? Thanks.

A car leaves town X at 0800 and arrives at town Y at 0915. During the first hour of the journey, the car travels at a constant speed of 80 km/h. If the average speed of the car between 0815 and 0915 is 2 km/h less than the average speed for the whole journey, find

(a) the distance of the journey from town X to town Y,

(b) the average speed between 0815 and 0915.

Here's my reasoning. I figured that if I assume x is the speed between 0900 to 0915 and then using the condition part of 2nd sentence, I would be able to solve for x. Here's the table I built,

$\displaystyle

\begin{tabular}{| l | c | c | c |}

Duration & Speed(km/h) & Time(h) & Distance(km) \\

0800-0900 & 80 & 1 & 80 \\

0800-0815 & 80 & 1/4 & 20 \\

0815-0900 & 80 & 3/4 & 60 \\

0900-0915 & x & 1/4 & x/4 \\

0815-0915 & 60 + x/4 & 1 & 60 + x/4 \\

\end{tabular}

$

Then, Avg Speed is

$\displaystyle

\begin{math}

\frac{80 + (60 + \frac{x}{4})}{\frac{5}{4}} = \frac{560 + x}{5}

\end{math}

$

And given,

$\displaystyle

\frac{560 + x}{5} - \frac{60+x}{4} = 2

$

Solving that equation gives me x = 1900 km/h!!!

Please help!, Where am I going wrong?

P.S. First time using this Latex stuff :), Thanks to great tutorial here.