Answer:
y = 1/2 * x + 4.5, both Sara and Brad were wrong
Step-by-step explanation:
Line pass (9,9) and (15,12)
y = mx + b
m = difference of y/ difference of x = (12 - 9) / (15 - 9) = 1/2
y = 1/2 * x + 4.5
check Sara: y=1/3x-2 (9,9) y = 1/3 * 9 -2 = 1 ≠ 9
check Brad (9,9) y = 1/3 * 9 + 6 = 9
(15,12) y = 1/3 * 15 + 6 = 11 ≠ 12