The most important part is checking to see if the second digit is positive or negative. If the number is negative, subtraction will be used. If positive, addition will be used. For this case, the best answer would be C.
As for the first row, its positive 3 and -6. Therefore, they should create the equation of:
3x - 6y = 15
As for the second row, its -7 and 5. They should create the equation:
-7x + 5y = 32
So, C is the best option.
