Six Common Writing Errors

Each sentence below illustrates one$-$and only one$-$common writing error. Some of the errors have to do with word choice, some have to do with punctuation, and some are about style. Read each sentence, determine what error it contains, and then, as simply and directly as you can, describe the error. Finally, edit the sentence to correct the error. $($Don$\text{'}$t rewrite the sentence, just cross out problems and write corrections above it$.)$

More than fifty people attended the party, and their were seven cakes of all kinds.

Description of error:

The family wanted to set aside one of the cake's for the birthday