Consider the following formula: a = 1/2 b - 4
Which of the following statements is true for this formula?
A. When the value of b is less than 8, a is negative.
B. When the value of b is greater than 8, a is negative.
C. When the value of b is less than 8, a is positive.
D. When the value of b is greater than 4, a is positive.