The option C) y = 15/x
a) y = 15 x is an example of direct variation, with proportionality constant = 15
b) is an example of linear variation (it is the equation of a straight line that does not pass through the origin)
c) y = 15/x => y*x = 15 = constant which is the characteristic of an inverse relation
d) y = x/15 is an example of an inverse relation, with proportion constant = 1/15
