Sort methods

[rs74]

a = add(multi(3));

a = a + mod(div(a + 3)) + sub(12)

How (and why) should this functions (add, multi, mod, div, sub) be sorted? I am thinking like this ->

1. multi (a = a) (first function)
2. mod (a + mod) (second function)
3. sub (a + mod + sub)
4. ?
5. ?