With the four equation evaluated symbolically I am getting results for 3 but the same is giving result as 0 for the last equation any idea?
And why do you think thats wrong?
The equation is linear in the first three variables you differentiate to, but constant wrt the last one. So the results seem to be correct.
Did you intend to differentiate the same expression to four different variables?
Then look at these expressions.
The first is different from the last three: it adds R.hcc to a quotient, instead of R.hch.
The 4th differential is to R.h, while R.h is not part of the expression, hence the result is 0.