We know that $Px = \lambda x$
So $(P^2 + 2P + I)x = P^2x + 2Px + Ix =\color{Brown}{ \lambda^2 + 2\lambda + 1}$
$\lambda_1 = -1$
$\lambda_2 = \frac{1}{2}$
$\lambda_3 = 3$
let $\lambda^{'} _1,\lambda^{'} _2,\lambda^{'} _3$ be eigen values of $(P^2 + 2P + I)$
$\lambda^{'} _1 = \lambda _1^2 + 2 \lambda _1 + 1 = (-1)^2 + 2(-1) + 1 = 1 + 1 -2 = 0$
$\lambda^{'} _2 = \lambda _2^2 +2 \lambda _2 + 1 = (\frac{1}{2}) ^2 + 1 + 1 =\large \frac{9}{4}$
$\lambda^{'} _3 = \lambda _3^2 +2 \lambda _3 + 1 = 3^2 + 2(3) + 1 = 16$