Question 1091242
Christopher ran m miles at r miles per hour and arrived on time.
time = {{{m/r}}}
 Then the distance was increased 7 miles.
(m+7)
 How fast did he have to run to travel the new distance in the same amount of time?
let s = the increase in speed required to do this 
{{{((m+7))/((r+s))}}} = {{{m/r}}}
cross multiply
m(r+s) = r(m+7)
distribute
mr + ms = mr + 7r
subtract mr from both sides
ms = 7r
s = {{{(7r)/m}}} mph the increase in speed
"How fast to run to travel the new distance in the same amount of time?  
r + {{{(7r)/m}}} mph is the required speed