Answer:
[tex] \boxed{a. \: f(x) = 3(2)x} \: is \: correct[/tex]
Step-by-step explanation:
[tex]if \: the \: points \: are \: (1, 6) \: and \: (2, 12) \to \\ then \to \\ m = \frac{12 - 6}{2 - 1} = \frac{6}{1} \\ \boxed{m = 6} \\ y - 6 = m(x - 1) \\ y = 6x - 6 + 6 \\ y = 6x = (3)(2)x \\ but \: y = f(x) \to \: hence \to \\ \boxed{ f(x) = 3(2)x}[/tex]