Question 920200
t = D/r
{{{300/x - 300/(x+10) = 1hr}}} |Multiplying thru by x(x+10)so as all denominators = 1
300(x+10) - 300x = 1x(x+10)
x^2 + 10x - 3000 = 0 (Tossing out the negative solution for unit measure)
(x+60)(x-50) = 0
x = 50mph.  New Speed 60mph  (50+10)
and...checking
6hr - 5hr = 1hr