How many quarter minutes does the second hand of a clock complete to travel through from 6:15 p.m. to 6:18 p.m.?

We know, 

One quarter minute = 15 seconds

Now, the time difference between 6:15 p.m. and 6:18 p.m. is = 3 minutes

So, One whole minute has 60 seconds, which means 

= 60 / 15 = 4 quarters 

So, 3 minutes will have = 4 × 3 = 12 quarter minutes.