Answer the following requirements for each separate case that involves contracts with performance obligations.

A retailer enters into a contract with a customer to sell an electric toothbrush, bundled with the replacement parts for the toothbrush. The retailer also sells the replacement parts and toothbrushes separately. The customer can use the toothbrush without the replacement parts, but the replacement parts have no use without the toothbrush. How many performance obligations exist in the bundling of the toothbrush and the replacement parts?