You should follow PEMDAS, meaning what ever is in parenthesis goes first. Then exponents, multiplication, division, adding, and last subtraction.
For example, 3(3x + 1)/2 = ____ [x = 3]
Parentheses: 3 x 3 = 9 + 1 = 10 (only reason why your adding 1 to it, is because you do everything in the parentheses.
Exponents: there is none so skip.
Multiplication: 3 x 10 = 30.
Now keep in mind in this example it would look like this so far (30 / 2 = _____)
Division: 30 / 2 = 15.
Adding: you skip! [because after following pemdas (in order) there is nothing left in the equation that is left to add]
Subtraction: skip as well, (because following pemdas, there would be nothing left to subtract).
Thus, your final answer in this example would be 15!