p(X=1)+p(X=0)=4P(X=2)e^(-λ)+λe^(-λ)=4 λ^2 e^(-λ)/2!2λ^2-λ-1=0 λ=3P(X=3)=λ^3 e^(-λ)/3!=9/2 e^-3
1/6e^(-1)
P(X=3)=e^(-1)/6