12 5/25 as a simplified mixed number would be 12 1/5
D is a notation for differential. There is a d2 in your formula because in the numerator there are two differentials. The formula is thus the second derivative of a function with respect to two variables.
0.015x+0.03(12000-x)=300
Solve for x
X=4000 at 1.5%
12000-4000=8000 at 3%
2 is the correct answer I'm almost definite
