Answer:
it the first choice you ate three chocolate independently
B. 24x2 is the correct answer
To find the number of years between 1844 to 2015 you have to subtract.
Lets say that x is the # of years in between 1844 and 2015
Then we have:

After doing the subtraction using a calculator or a pencil and paper, you get that:

So 171 years have passed from 1844 to reach to 2015.
You are told that sprinklers run for the same amount of time. lets refer to this time as T.
you are told that 4 sprinkles run one at a time for 50 minutes total. that means that T should be 50/4 = 12.5 minutes = 12 minutes and 30 seconds