Forming an equation (solved)

A Music Store sells sets of CDs of equal value for $18.

I) Taking x to be the number of Cds in each set, write down an expression in x to represent the price of each CD.

The store reduces the number of Cds in each set by 3 and reduces the price in each set by $6.

II) Write down an expression in x to represent the new price of each Cd in a set

The Price in this case, has increased by $1

iii) write and equation to represent the above info and solve for x.

The answer I got for (i) was 18/x and (ii) x-3/12,

But then at part three would it be 18/x = x-3/13

or something like 18/x = x-3/12 + 1

edit: Solved it, I put x-3/12 = 18/x + 1 and then after working that out I got -9 and 6, and since the answer cant be minus, I got $6