If the cost of x metres of wire is d rupees, then what is the cost of y metres of wire at the same rate?

$$\eqalign{ & {\text{Cost of }}x{\text{ metres}} \cr & = {\text{Rs}}{\text{. }}d \cr & {\text{Coast of 1 metre}} \cr & = {\text{Rs}}{\text{.}}\left( {\frac{d}{x}} \right) \cr & {\text{Cost of }}y{\text{ metres}} \cr & = {\text{Rs}}{\text{.}}\left( {\frac{d}{x} \times y} \right) \cr & = {\text{Rs}}{\text{.}} {\frac{{yd}}{x}} \cr} $$