I tried working the 6MS #2 HVAC and cant figure out why they chose 32 Btu/lbm over 28. I worked it exactly the same way as the US solution of ex 38.4 and it should give me the same result as the method they used. I used 13.65 for vb from psych chart giving me 5000/13.65 = mb = 366 lbm/min. I used 14.2 for va giving me 2500/14.2 = ma = 176 lbm/min. Using the mixing equation (eq 38.21) I got a Tmix = 80 F or so. Going back to the psych chart and got pretty much 28 for the final answer. Any thoughts? Maybe I just have to squint harder and this tiny psych chart I'm using in the MERM.