Reading enthalpy of mixing graph

I'm struggling to interpret enthalpy of mixing data. Given this plot, [![enthalpy of mixing of ethanol and water](https://i.stack.imgur.com/lgSbi.png)](https://i.stack.imgur.com/lgSbi.png) from [this paper](http://pubs.acs.org/doi/abs/10.1021/je60034a008), say I want to calculate the heat released from mixing 0.29 mol of 7.7% ethanol with 0.71 mol of 28.7% ethanol to get 1 mol of 22.6% ethanol.


Is it correct to say $\Delta h\_m = 753 - (0.29\*605 + 0.71\*672) = 100 J/mol$?


Or, in other words, can I subtract the molar weighted enthalpies of mixing at the initial states from the enthalpy of mixing at the final state to get the change of enthalpy of mixing from that process?


It seems trivial, but something about it feels weird.


