Write an equation and then solve it?

Question

A semi truck travels 300 miles through the flatland in the same amount of time that it travels 180 miles through the Great Smokey Mountains. The rate of the truck is 20 miles per hour slower in the mountains than in the flatland. Find both the flatland rate and mountain rate.

Answer 1

Distance = rate * time

Flatland equation

300 = rt

Mountain equation

150 = (r - 20)t

Solve for t and graph both

t = 300/r
t = 150/(r - 20)

The point of intersection is (40, 7.5)

So r = 40 mph
The time is 7.5 hours

Flatland rate is 40 mph
Mountain rate is 20 mph

Answer 2

Someone else submitted this last week. The answer hasn't changed.
Let x be the mountain speed
Then x+20 is the flatland speed.
The equation we use is time = distance/speed.
For the mountain: t = 180/x
For the flats: t = 300/(x+20)
Since the two times are equal, we can set what they are equal to equal to each other. Or
180/x = 300/(x+20)
You can do the rest.