The measured data is
x=[10.56, 9.52, 9.73, 9.80, 9.78, 10.91].
Calculate the mean.
m = (10.56+9.52+9.73+9.80+9.78+10.91)/6 = 10.05
Calculate the deviations from the mean.
k = x - m
= [0.51, -0.53, -0.32, -0.25, -0.27, 0.86]
Calculate the absolute deviation from the mean.

Answer: 0
The tree was approximately 40.8ft tall.
You use the equation, a^2+b^2=c^2.
12^2 + 39^2 = x^2, add the results of 12^2 and 39^2 to make 1665 = x^2. You can take the positive root of both sides, 3√185, and it equals 40.80441152, which is rounded to 40.8.