Answer
50 mph on flatlands, 30 mph in mountains
Work Step by Step
flatland: 300 miles at a rate of x (in t hours)
mountains: 180 miles at a rate of $x-20$ in (t hours)
$300 = x*t$
$180 = (x-20)*t$
$300 = x*t$
$300/x = x*t/x$
$300/x = t$
$180 = (x-20)*t$
$180/(x-20) = (x-20)*t/(x-20)$
$180/(x-20) = t$
$300/x = 180/(x-20)$
$180x = 300*(x-20)$
$180x = 300x-6000$
$180x + 6000 = 300x$
$6000 = 120x$
$6000/120 = 120x/120$
$x = 50$
$x-20$
$50-20$
$30$
