Answer
$\frac{3}{4}$ the total energy
Work Step by Step
$$E_{total}=\frac{1}{2}kA^2$$ $$U=\frac{1}{2}kx^2=\frac{1}{2}k(\frac{A}{2})^2=\frac{1}{8}kA^2$$ $$KE=E_{total}-U=\frac{1}{2}kA^2-\frac{1}{8}kA^2=\frac{3}{8}kA^2$$ The fraction of total energy that is kinetic energy is given by $$\frac{\frac{3}{8}kA^2}{\frac{1}{2}kA^2}=\frac{3}{4}$$