Precipitation calculation?

A solution contains 0.03 mol L-1 Ba++ and 0.03mol L-1 Ca++. What concentration of CrO42- will precipitate the maximum amount of BaCro4 without precipitating any CaCrO4? The K sp values are BaCrO4 1.2X10-10 and CaCrO4 7.1 X 10-4.