this Keyword in Different Contexts

const calculator = {
  value: 0,
  add: function(n) {
    const helper = function(x) {
      this.value += x;
    };
    helper(n);
  }
};

Using var self = this
Using call/apply
Both A and B
Inner function 'this' can be fixed by: 1) Storing outer 'this' in closure variable, 2) Using call/apply with stored 'this', 3) Converting to arrow function, 4) Binding function explicitly, 5) Each approach has specific use cases, 6) Common problem in nested functions.
Neither approach works