R. B. Greaves, an R&B singer whose 1969 hit “Take a Letter, Maria” reached No. 2 on the Billboard pop chart, died on Thursday in Los Angeles. He was 68. His death was confirmed by his son, Shiloh Greaves. “Take a Letter, Maria,” which Mr. Greaves wrote, is about a hard-working man who dictates a “Dear Jane” letter to his secretary after coming home to find his wife “in the arms of another man.” He sings, more in acceptance than in anger: “So take a letter, Maria, address it to my wife/Say I won’t be coming home, gonna start a...