Calculate the concentration in mol per litre of ammonium ions in a solution solution prepared by mixing 360.0mL of 0.250 mol per litre ammonium sulphate solution with 675.0mL of 1.20mol per litre ammonium nitrate solution. Assume solution volumes are additive.

I got 0.870 mol per Litre...

I don't think it's correct....

mols (NH4)2SO4 = LxM = 0.360L x 0.250M =??
mols NH4NO3 = LxM = 0.675 L x 1.20 M = ??

M NH4^+ of final solution = mol/L
total mols NH4^+ = 2 x mols of (NH4)2SO4 + mols NH4NO3 = ??
total volume = 0.350L + 0.675 L = ??