See Murphy Library's Citing sources guide for comprehensive guidance to MLA style.
Your assignment is to write an Innovative Proposal Argument.
Your paper may use informational sources to provide background on your issue or to support the proposal you're making, but your paper will also need opinion/argument sources that show multiple perspectives on the problem that you're proposing to solve.
This guide offers recommendations both for informational sources and also for opinion/argument sources from among resources available through Murphy Library.