Equilibrium: JEE Main 2009 Chemistry question

Solid Ba(NO₃)₂ is gradually dissolved in a 1.0 $\times$ 10⁻⁴ M Na₂CO₃ solution. At what concentration of Ba²⁺ will a precipitate begin to form ? (K_sp for BaCO₃ = 5.1 $\times$ 10⁻⁹ )