CONCEPT: The question tests on the basic concepts of Unitary method.

Marla is 20 laps ahead of Nick every hour.
4 more laps is 20% or 1/5 th of 20.

If 20 laps is the difference for 1 hour, i.e 60  min (100%)
4 laps(20%) as difference shall occur in  =60/20 *4
=12 min. (Option C) and you may not have to use any advanced concept of R.S here.