Add the data=432, then divide by 6=72 is the mean.
Subtract the mean from each value and square the result:
52 25
(-7)2 49
(-12)2 144
52 25
(-9)2 81
182 324
Add the squares: 648, divide by 6=108 is the variance.
Standard deviation=√108=10.39 approx is the standard deviation.