5 students of a class have an average height 150 cm and variance 18 cm^2. A new student, whose height is 156 cm, joined them. The variance (in cm^2 )…

$\displaystyle 5$ students of a class have an average height $\displaystyle 150$ cm and variance $\displaystyle 18 \mathrm{~cm}^2$. A new student, whose height is $\displaystyle 156$ cm , joined them. The variance (in $\displaystyle \mathrm{cm}^2$ ) of the height of these six students is :