[tex]x \: \alpha \: y \\ \\ x = ky[/tex]
When x = 2 and y = 4, substitute
[tex]2 = 4k \\ \\ k = \frac{2}{4} = \frac{1}{2} [/tex]
That's the constant of variation
When x = 0.5; using the constant as 1/2:
[tex]x = ky \\ \\ x = \frac{1}{2} y \\ \\ 0.5 = \frac{1}{2} y[/tex]
[tex]y = 2 \times 0.5 \\ \\ y = 1[/tex]
That's the value of y when x = 0.5
