An equation of a parabola is usually in the form f(x)=ax^2+bx+c, so look for equations in this format.
Is there a picture I can look at?
The correct answer is B. The function has a constant rate of change, decreasing for all x at a rate of 6.
In order to find the rate of change, we have to identify the slope. The slope is always the coefficient of x when in slope intercept form. In this case it is -6, which means it decreases at a rate of 6.