One small thing I can see immediately
you wrote;
(100 g H2O) x (4.18 J/gK) x (37.5 - 25)K = 5486.25 J
but this should actually be;
(100 g H2O) x (4.18 J/gK) x (37.5 - 25)K = 5225 J
or
(105 g H2O) x (4.18 J/gK) x (37.5 - 25)K = 5486.25 J
I don't know if this helps but it's what I could...