What does this program print?

What does this program print?

const balance = {
  [Symbol.toPrimitive](hint) {
    return hint === 'string' ? '12 credits' : 12;
  },
};

console.log(String(balance), balance + 3);

1. 12 credits 15
2. 12 credits 123
3. 12 15
4. It throws because Symbol.toPrimitive cannot return different primitive types.