How did indentured servants servitude benefits the colonies?

Indentured servants worked for 7 years with a promise of their own land. Eventually this ceased do to over population and fights with the Indians. Which brought in the issue of Slavery, Slaves had no rights, however and Indentured servant had the rights. Also with Slavery they weren't promised land, you didn't have to pay them, plus the set of time they worked for you was infinite. 

Indentured servants benefited the colonies, because it help them build up and they also were able to expand when their contract was up.

Choices? multiple choice

Your answer is b , public works