Answer
$K = 1.0~J$
Work Step by Step
We can use conservation of energy to find $K$ when $y = -10~cm$:
$K+U_g+U_e = 0$
$K = -U_g-U_e$
$K = -mgy-\frac{1}{2}ky^2$
$K = -(20~N)(-0.10~m)-\frac{1}{2}(200~N/m)(-0.10~m)^2$
$K = 2.0~J-1.0~J$
$K = 1.0~J$