Question 748447
let the speed of first car is x
then the speed of second car is x-5

then the time takes by the first car 

{{{speed = distance/time}}}
{{{x=300/time}}}
{{{time= 300/x}}}

time takes by the second car

{{{speed = distance/time}}}
{{{x-5=275/time}}}
{{{time= 275/(x-5)}}}

as given that this two time are equal
{{{300/x= 275/(x-5)}}}
{{{300(x-5)=275x}}}
{{{12(x-5)=11x}}}
{{{12x-60=11x}}}
{{{12x-11x=60}}}
{{{x=60}}}

so the speed of two cars are 60mph and 55mph