Embedded with commentary and reflections on history, art and life, Xaviera Simmons’ Number 16 (2013), is a mesmerizing and demanding video work, on view at the Kemper Museum of Contemporary Art. The 60-minute split-screen piece presents side-by-side performances, one by the Brooklyn-based artist, who creates an abstract expressionist painting; the other by a female vocalist, who sings her heart out.