Question 103093
The idea here is to substitute the new value into the function.

Usually, f(x) is the function, but this time it is g(x).

We are told, g(x) = 5x - 2.

That is the function. Think of it like a machine that takes some input and multiplies it by 5 and then subtracts 2: Input x and out comes 5x-2.

Here were are told to find g(3a), so they are telling us that x=3a. Simply substitute: Plug in 3a to the "function machine" and out comes 5 times 3a - 2:

g(3a) = 5(3a) - 2

g(3a) = 15a - 2