If x₁, x₂, … , x_n are observations with frequencies f₁, f₂, … , f_n i.e. x₁ occurs f₁ times and x₂ occurs f₂ times and so on, then we have

mean() of observations is given by

Given, mean = 8.1

Putting this values in formula:

⇒ 162 = 132 + 5k

⇒ 5k = 30

⇒ k = 6