To convert £280 at the post office exchange rate of £1=€1.17, you calculate: 1£: 1.17€ = 280£: x. Thus, x = 1.17 * 280, giving us x = 327.6 €. Verification shows this calculation is sound.
This statement is incorrect.
In f(3x), the input 'x' is multiplied by 3 prior to being substituted into the function.
Conversely, with 3f(x), the result (output) is multiplied by 3 after you have calculated the output from the input value.