LAWRENCE – A man who confessed to selling drugs out of a local grocery store on Chatham Street in Lynn in 2009 is headed to state prison for up to four years.Michael Castillo, 26, last known address of 22 Inman St., #1, Lawrence, was about to go on trial Tuesday morning on drug and firearm charges, but instead pleaded guilty in Lawrence Superior Court in a deal worked out by his attorney, Carl Donaldson, and prosecutor Marsha H. Slingerland.By making the deal, he avoided going to trial and facing up to 15 years in state prison.Castillo pleaded guilty to possession of marijuana with the intent to distribute, second offense, possession of marijuana within 1,000 feet of a school and carrying a firearm without a license before Judge Richard H. Welch, III.He was sentenced to serve not less than two and a half years and not more than four years in state prison.The judge also imposed another two years in jail for the handgun possession charge, but he has already served that sentence awaiting trial and it was imposed to run simultaneously with the state prison term.The judge adopted the joint sentence agreement proposed by the prosecutor and defense.On Aug. 16, 2009 Lynn police detectives raided Martina’s Grocery, located at 391 Chatham St., and found Castillo working alone in the store with a loaded Glock 29 10mm handgun under the counter with 10 bullets in the magazine.In addition, a black plastic bag with what looked to be marijuana was discovered next to the handgun.A mixed-nut container containing more than 50 zip bags of marijuana was found behind the counter and approximately a quarter of a pound of marijuana was discovered in the bathroom.