Hey trustnoone and welcome to the forums.
In short the answer is BODMAS (Brackets Division Multiplication Addition Subtraction)
Basically evaluate all the bracketed terms first and then use the DMAS rules.
Inner brackets get evaluated before outer brackets, but in the end once you evaluate the brackets then you just evaluate the expression using the DMAS ordering.
It doesn't fail and its easy to remember :)
Also if you use things other than arithmetic (like exponentiation) then you need to adjust for that as well.