Hi afpskierx,
Have you find the [itex]u_2[/itex] by doing interpolation? I got the answer for [itex]u_2[/itex] = 3047.35 kJ/kg
At state 1, I don't quite understand with the question which stated that that mass of saturated mixture of water is 12kg.
So, I assume the quality, x = mass of vapour / total mass. You will get 7.2kg for your mass of vapour.
At state 2 (which is the [itex]P_2[/itex] = 400kPa and [itex]T_2[/itex] = 450 C) I assume it SUPERHEATED VAPOUR seems the [itex]T_2[/itex] larger than saturated temperature.
I just can help for what I wrote above. Otherwise, I'll try come out for the full solution later.