Covariance between Index A and B calculator, between, numbers, please, points

wildrose

A:
-6.4
6.6
12.9
3.2

B:
-6.2
19
-7.7
4


It asks for the covariance...I plugged the numbers into their respective data points in my calculator and got 10.37...wrong answer. Correct answer was 13.82

The explanation says, when done out by hand, you would use n-1 in the denominator when dividing the summation of all the covariances...i thought this was only done for samples?

Help please, thanks.