For f(x), when x=1, y=1, and when x=2, y=4. Since the graphs are both quadratic, you can assume f(x)=x².
For g(x), when x=2, y=1, and when x=4, y=4. So g(x)=(x²)÷4.
Now it's a given that g(x) is equivalent to f(k*x), so we can say
(x²)/4=(kx)²
4kx²=x²
k=1/4
