Final answer:
The new function after shifting f(x) = 2x - 4 down by three units is f(x) = 2x - 7, which corresponds to option (a).
Step-by-step explanation:
The student has asked what the new function is if the function f(x) = 2x - 4 is shifted three units down. When a function is shifted down by some units, you subtract that number from the entire function. In this case, you subtract 3 from the original function, resulting in the new function being f(x) = 2x - 4 - 3.
By simplifying the expression, you get f(x) = 2x - 7, which makes option (a) the correct answer.