Answer
faster car is 78 1/3 mph, slower car is 68 1/3 mph
Work Step by Step
rate * time = distance
faster car: rate of $x$, time is 3 hours
slower car: rate of $y$, time is 3 hours
distance between cars is 440 miles
faster car is 10 miles per hour faster
$3x+3y=440$
$y=x+10$
$3x+3y=440$
$3x+3(x+10)=440$
$3x+3x+30=440$
$6x + 30=440$
$6x=410$
$6x/6 =410/6$
$x= 68.3333$
$y=x+10$
$y=68.333+10$
$y=78.333