when did he begin his career?
She began her career by recording for Mercury on January 22, 1976
Reba McEntire
McEntire made her first recordings for Mercury on January 22, 1976, when she released her debut single. 
who is reba mcentire? An American country singer, songwriter, actress, and record producer.
wiki:19551155
Reba McEntire [SEP] 1976–83: Career launch at Mercury
McEntire made her first recordings for Mercury on January 22, 1976, when she released her debut single. Upon its release that year, "I Don't Want to Be a One Night Stand" failed to become a major hit on the "Billboard" country music chart, peaking at number 88 in May. She completed her second recording session September 16, which included the production of her second single, "(There's Nothing Like The Love) Between a Woman and Man", which reached only number 86 in March 1977. She recorded a third single that April, "Glad I Waited Just for You", which reached number 88 by August.