First review the forms of the indefinite articles and ein words in all the cases and genders. - Click Here
Then review the endings of the adjectives that follow ein words. The following website is a German one and is slightly different than the way we have been learning the adjective ending declensions. Click here.
Now, you can attempt this assignment. Follow the example closely. I give you the gender of the noun in question. You must determine the proper case.
Example:
________________________ bringt den Kuchen und die Getränke. (Mädchen / nett
Ein nettes Mädchen bringt den Kuchen und dei Getränke.