[Enrique]

Well the technique of "every second they get 4.5 meters closer" from IamSam is easier to understand.

Then the answer for how long is just 20 / 4.5 = 40/9 = 4.444

And distance is just that times 2, so 8.888.

Seems easier for a remedial student to understand, and you don't deal with fractions.