👨‍💼 Perfect! You've seen the difference between let and const in action.

When you tried to reassign TAX_RATE, TypeScript caught it immediately:

Cannot assign to 'TAX_RATE' because it is a constant.

This is exactly what we want! The tax rate shouldn't change during the program's execution, and const enforces that.

🦉 Notice how cartTotal needed to be let because we updated it multiple times. The pattern of accumulating a total is a classic use case for let.