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

**SOLUTION:**

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.