Pete drove from Buffalo to Boston a distance of 720km On ret

Pete drove from Buffalo to Boston, a distance of 720km. On return trip he increased his speed by 10km/h. If the total trip took 17h, what was his speed from Boston to Buffalo?
I\'m having trouble working it out, I begin with this:
I start with (720/x)+(720/x+10)
Expanded it to: 17x^2 - 1270x + 7200
Speed I got next using the quadratic equation: 62.5
But thats apparently wrong, what am I doing wrong?

Solution

(720/r) + 720/(r+10) = 17
720r + 720(r+10) = 17r*(r+10)
1440r + 7200 = 17r^2 + 170r
17r^2 - 1270r - 7200 = 0