Step-by-step explanation:
what do mean by 3* ?
do you mean 3 to the power of x ?
then the answer is x=2, as 3² = 9.
but if not, we have no clue, what f(x) truly is.
maybe it is 3 × x ?
then the answer would be x=3, as 3×3 = 9.
and so on. again just poking in the complete dark ...