This problem is quite simple, I'll try to help you understand why it is~
f(x) is NOT f times x, but it is f, the function of x.
This means that the value of f depends on the value of x. f(1) means the value of the function, f, when x = 1.
Thus, f(3) is the value of the function, f(x), when x = 3. According to the table, f(x) is 1 when x is 3. That should be your answer.
Please do let me know if you still do not understand.
Happy Studying~
