Answer: Second choice; f(x) = -3x + 4
Step-by-step explanation:
You pretty much want to isolate y, f(x) is also acceptable as y. The term f(x) means the value of the function when you input the x value.
Subtract 9x from both sides to get 3y = 12 - 9x, then divide everything by 3 in order to get y completely alone. You get y = 4 - 3x or f(x) = 4 - 3x
Different way you could potentially write this answer:
y = 4 - 3x
y = -3x + 4
f(x) = 4 - 3x
f(x) = -3x + 4
Each one equals each other and are all perfectly acceptable