Business requirement

A courier application must calculate delivery charges using a base zone price, an extra-weight charge, and an optional express multiplier.

1. Use base charges of ₹50 Local, ₹100 National, and ₹250 International.
2. For weight above 5 kg, add ₹20 for every additional kg.
3. If Express is selected, multiply the calculated charge by 1.5.
4. Apply the rules in the correct order: base, extra weight, then express.
5. Reject zero or negative weight.