First....find the mean = [ 4 + 16 + 21 + 32 + 11 + 12 ] / 6 = 16
Calculate the sum of the squared differences between the mean and each data point
(4 - 16) ^2 = (-12)^2 = 144
(16 - 16)^2 = 0^2 = 0
(21 - 16)^2 = 5^2 = 25
(32 - 16)^2 = 16^2 = 256
(11 - 16)^2 = (-5)^2 = 25
(12 - 16)^2 = (-4)^2 = 16
Add these = 144 + 0 + 25 + 256 + 25 + 16 = 466
The variance = √ [ 466 / nuumber of data points ] = √ [466/6 ] ≈ 8.81