The mean and variance of plant height of two highly inbred strains (P₁ and P₂) and their progeny (F₁ and F₂) are shown here.

   Strain     Mean (cm)     Variance  _
     P₁           34.2                 4.2
     P₂           55.3                 3.8
     F₁           44.2                 5.6
     F₂           46.3               10.3

Calculate the broad-sense heritability (H²) of plant height in this species.