@rihnavy,
If I understand your problem correctly, you have your formula slightly wrong.
z = (x̄ - μx̄)/σx =( x̄ - μx̄)/(σ/√n) = (12,749 - 12,752)/ (1.2√35) = -14.8
If you look up this z score in a table or just use
an internet calculator, you see that the chance of being fourteen standard deviations from the mean is zero. Since that is a really unusual answer, it makes me wonder if I read it correctly.