Fuel Additive for Gas Mower?

We bought a Poulan push mower around May or June; it worked fine till around August. My husband had neighbor look at it and he cleaned, I think, the filter and then added some kind of treatment to the gas.

He said the ethanol causes problems. Of course, my husband didn't ask what was put in and the neighbor is away. We are both challenged when it comes to this kind of stuff.

By Linda from Onancock, VA