1.) 2 L x 1.50 mol/L = 3 moles
2.) 0.15 L x 1.35 mol/L = 0.2025 moles
3.) 0.2 L x 3.00 mol/L = 0.6 moles; 0.3 L x 1.50 mol/L = 0.45 moles
total moles = 0.6 + 0.45 = 1.05 and total volume = 0.2 L + 0.3 L = 0.5 L. Final concentration = 1.05mol/0.5L = 2.1 M