stretching reciprocal graph

Question

How do i show that the curve $y=\frac a{x^2}$ is a horizontal stretch of the curve $y=\frac 1{x^2}$ and how do i find the stretch factor? i have tried and added k constant in front of $x^2$, so $y=\frac a{kx^2}$ but not sure where to go from there.