Hi there!
y ∝ x
∴ y = kx ---(i)
Where " k " is the constant of variation & k ≠ 0
Now to determine " k ".
Use the given condition that when :
• x = 4
• y = 20
Substitute th' respective values in Eqn. (i) :-
y = kx
⇒ 20 = k(4)
⇒ 4k = 20
⇒ k =

= 5
Hence,
The constant of variation for the relation is 5
~ Hope it helps!