There is a generally accepted order of computations: parentheses, exponentiation, multiplication, division, addition subtraction (PEMDAS. for which the mnemonic is please explain my dear aunt sally).
In your first example, the multiplication would be done first and then the additions and subtractions. No parentheses are necessary except to be pedantically clear. The same is true in your second example.
Now, having said that, I want to be clear: it is always acceptable to add parentheses for clarity and in some cases it is essential. For example: 1/3x+1. Strictly speaking this should be interpreted as (1/3x) + 1, i.e. division before addition, BUT what is often intended is 1/(3x+1) and if that is what you mean, parentheses are the only way to write this correctly!
