At 350 F I'd estimate 25 minutes per pound but verify with a meat thermometer. Three pounds would figure to 75 minutes (1 hour 15 minutes). Check the temp at 60 minutes. Pull the roast out at 135-140 F internal temp and let it rest, covered for 20 minutes before carving.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan