The ratio of the y-value to the x-value is the same in every case (1.6), so the variation is direct and the constant (k) is 1.6.
[tex]\dfrac{y}{x}=\dfrac{6.4}{4}=\dfrac{11.2}{7}=\dfrac{16}{10}=\dfrac{20.8}{13}=1.6[/tex]
Multiplying the above equation by x, you get
... y = 1.6x
