The answer is C.
To solve these types of equations you first need to make sure that you equation is equal to 0. In this case all of the numbers are already on the same side so no work needs to be done there. Then we can get a, b and c values for the quadratic equation by looking at the coefficients.
a = 4 (number attached to x^2)
b = -6 (number attached to x)
c = 1 (number with no variable attached)
Now we can put this into the quadratic equation.


The answer would be 15,120
I believe that the question is assuming this is taking place over one month here is what I think you would do.
1) 75/12.5 = 6
2) add that answer to 75, so 75+6, and you get 81
Find the difference
5/6-3/4 (you have to get the same denominators by multiply the individual fractions)
(5/6)*2 and (3/4)*3 to get a denominator of 12
10/12-9/12 (subtract numerators, leave denominator)
=1/12 which is the answer
Hope this helps<span />