We need to apply "Distributive Property" in order to get rid of the grouping symbols in the algebraic expression.
Such means to multiply 3 by each of the terms inside the parenthesis. That is:
3 times x and then 3 time 4:
3 times x remains as "3 x" since we don't know the value of "x", and 3 times 4 becomes 12:
3 (x+4) = 3 x + 12
Which seems to be the second option you listed.