If the variation is proportional dividing the y-value by the x-value will give the same result for all table entries. That quotient is the constant of variation (k).
Here 6.4/4 = 11.2/7 = 16/10 = 20.8/13 = 1.6
The value of y varies directly as x, and the constant of variation is 1.6. The equation is ...
