The answer:
1. depends on compiler/interpreter design in a computer machine...
e.g. multiplication is commutative but division is not! This raises the issue about associativity in interpretation/compilation...
2. depends on operation definition ...
"ab" = a times b but "12" = 1 times 10 and then plus 2 in a decimal system...
It becomes the issue of operational assumptions.
3. The order of operational precedence (e.g. forced operations over arithmetics) needs to be defined before any meaningful interpretation of computation of the given formula/expression can occur.