HUDSON, MASS. — Brokerage firm Horvath & Tremblay has arranged the $21.9 million sale of Center at Hudson, an 84,605-square-foot shopping center located about 30 miles west of Boston. The grocery-anchored center consists of a freestanding, 58,266-square-foot Stop & Shop, which has operated out of that location since 1990 and recently extended its lease, and 26,339 square feet of inline space. Bob Horvath and Todd Tremblay of Horvath & Tremblay represented the seller and procured the buyer, both of which requested anonymity, in the transaction. The deal traded at a cap rate of 6.35 percent.