Donnel designs inc., an interior decoration firm, enters into a partnership with casca paints inc. as a result, customers can now get a complete interior design solution for their houses. this is an example of a

    Strategic alliance

Explanation:  A strategic alliance is an agreement between two, say, companies to enter together into a business project that will benefit both companies / parties. In this type of business alliance, the two parties / companies remain independent and this agreement is not overly complex, since there is no pooling of resources for starting a new company, each company has its own resources independently, but in cooperation with another company with which it has entered into a strategic alliance.

This is an example in this case because an interior decoration company that performs works in that area with its resources has entered into a strategic alliance with an interior painting company, therefore also with its own resources, and each of the companies remains independent in this agreement.