1. 0.4y = x is a direct proportion. It'd be more appropriate to write this as
y = x / 0.4, or y = 2.5x, in which case 2.5 is the constant of proportionality.
2. x = 1 - 2y is not a direct proportion because of the offset (1). A line representing a direct proportion must go through the origin (0, 0); this particular line does not do that.
