An 18-year-old man pleaded guilty to two charges for convincing a 13-year-old St. Clair Shores girl to send him a nude selfie over social media then blackmailing her.Hadi Cherri of Dearborn admitted in Macomb County Circuit Court on Thursday to extortion and accosting a child for immoral purposes in exchange for dismissal of two computer crimes, as part of a plea deal with Macomb prosecutors.