The correct Active/Passive form of the given sentence is:

☀ The cooking used to be done by Mary.

Explanation for other options:

☀ The cooking used to be doing by Mary. This option is not grammatically correct. The correct passive form should use "done" instead of "doing" to indicate that the action is completed.

☀ The cook used to been done by Mary. This option is not grammatically correct. It is not a passive construction, and "been done" does not fit in the sentence.

☀ The cooking used to be doing by Mary. This option is not grammatically correct. It uses "doing" instead of "done" to form the passive voice, which is not correct. The correct form should be "The cooking used to be done by Mary."