Which of the following is an example of derived demand?

Use the information below to answer the question that follows.

When commodity X sold for N25 per unit, 50 units of commodity Y were purchased. With an increase in the price of commodity X to N50 per unit, the demand for commodity Y fell to 20 units.

Determined the cross elasticity of demand?

Use the information below to answer questions.
When commodity X sold for N25 per unit, 50 units of commodity Y were purchased. With an increase in the price of commodity X to N50 per unit, the demand for commodity Y fell to 20 units.

The two commodities can be classified as?