Complex sentence: On April 13,2015 Anderson declared for the 2015 NBA draft, forgoing his senior year and on June 25,2015, he was selected by the Dallas Mavericks with the 21st pick of the 2015 NBA draft.
Split into simpler sentences: On April 13,2015 Anderson declared for the 2015 NBA draft, forgoing his senior year. On June 25,2015, he was selected by the Dallas Mavericks with the 21st pick of the 2015 NBA draft.