The answer is A.
See the attached photo for the steps, and let me know if you have any questions!
For this case we have to:
x: Be the variable that represents the largest number
y: Be the variable that represents the smallest number
We propose a system of equations:

From the first equation we have to:

Substituting in the second equation:

We look for the value of "x":

Answer:
C. They are equal to each other I think
Your answer would be x^2 - 3x + 15