Dear student,
Let first zero of polynomial is P and 2nd is 2P.
sum of zeros = - (coefficient of x )/(coefficient of x²)
P + 2P = - (-3K)/1 = 3K
P = K ------(1)
again,
product of zeros = constant/coefficient of x²
P.2P = 4K/1
2P² = 4K
P² = 2K
put equation (1) value
(K)² = 2K
K(K -2) = 0
K = 0, and 2
Thank you