Fiona recorded the number of miles she biked each day last week as shown below.

4, 7, 4, 10, 5

The mean is given by m=6. Which equation shows the variance for the number of miles Fiona biked last week?

a. s² = (4-6)²+(7-8)²+(4-6)²+(10-6)²+(5-6)²/6
b. σ = √(4-6)²+(7-8)²+(4-6)²+(10-6)²+(5-6)²/5
c. s = √(4-6)²+(7-8)²+(4-6)²+(10-6)²+(5-6)²/4
d. σ² = (4-6)²+(7-8)²+(4-6)²+(10-6)²+(5-6)²/5