The answer is 24 because you have to do 6x4=24
First part its 4C2 = 4*3 / 2 = 6
Second part
12 * 100
---------- = 4.3 %
280

this formula is used to determine gpm (gallons per minute) of flow with a known hose diameter (d) and nozzle pressure (np). The constant (29.7) is consistent when figuring flow with in gallons with a know pressure expressed in psi (pounds per square inch).
Scenario example: a firefighter is using a handline to fight fire with an 1 3/4 inch line with a nozzle pressure of 100 psi. How much water is the firefighter flowing when fighting fire?
Simple, first find a common denominator, 24.
So,
7/4*6= 42/24
and
5/6*6=30/24
Then just add,
42/24
+
30/24
Making it 72/24.
72/24=3
Thus, your answer is, 3.