Many example exercises fit the form of this one.
Two cyclists leave a city at the same time, one going east and the other going west. The westbound cyclist
bikes k mph faster than the eastbound cyclist. After t hours, they are d miles apart. How fast is each
cyclist riding?
One unknown variable, x, the speed for the eastward cyclist
All other numbers are given.
SPEED TIME DISTANCE
EASTWARD x t xt
WESTWARD x+k t t(x+k)
TOTAL d