Answer
Constant of variation or proportionality = 0.04
Step-by-step explanation
We are told that F varies jointly as q₁ and q₂ and inveresely as the square of d.
In mathematical terms,
F ∝ (q₁q₂/d²)
Introducing the constant of variation ot the constant of proportionality, k
F ∝ (q₁q₂/d²)
F = (kq₁q₂/d²)
We can then solve for k
If F = 80 when q₁ = 4, q₂ = 20 and d = 0.2
F = (kq₁q₂/d²)
80 = [(k × 4 × 20)/0.2²]
80 = (80k/0.04)
Cross multiply
80k = 3.2
Divide both sides by 80
(80k/80) = (3.2/80)
k = 0.04
Hope this Helps!!!