Two truck drivers leave a cafe at the same time, traveling in opposite directions. one truck goes 1 mph faster than the other one. after 3 hr, they are 291 miles apart. how fast is each truck going?

So hmmm notice, let's say  two, trucks, truck A and truck B,
so truck B is going faster by 1mph than truck A

notice, the distance between them is 291 after 3hrs,
that means, both truck drivers, have been driving for 3hrs,
and covered both combined 291,
let us say, A covered distance "d", so, B covered the rest of it,
or 291 - d,
though their distance and rate differs some, their driving time is
the same 3hrs though
thus 

solve for "r", that's how fast truck A was going

what about truck B?  well, B was going r + 1

It creates dogx^2 and then flip your answer and multiply by 2