Final answer:
The value of g that makes the equation true is 3.
Step-by-step explanation:
To find the value of g that makes the equation true, we need to expand and simplify the left side of the equation. The expanded form of (x+7)(x-4) is x^2 + 3x - 28. Comparing this to the right side of the equation, which is x^2 + gx - 28a, we can see that the coefficient of x is 3 on the left side and g on the right side. Therefore, the value of g that makes the equation true is 3 (option c).