Answer:
f(x)=x+3
Explanation:
In the table, you are looking for a repeated patten between x and f(x).
By the first row, you have 0, which you input and get three. This could be a number of formulas (since any number multipled by 0 is 0), but it clarifies that somewhere in the equation is a plus 3 (+3), since no matter what the number you multiply it by, you'll end up with 0 to which you add three.
Moving to the second row, we have 1, which we input and get four. This also means we have added three, so we couldn't have multiplied the number by anything other than one.
Testing this out, this works for the other two given examples. (2x1=2+3=5) and (3x1=3+3=6).
So you have f(x)= 1x+3
Which is also, f(x)=x+3.