For a better understanding of the solution/explanation given here please go through the graph in the file attached.
It is given that Alison sets aside $55 each month to spend on books and cd. Thus, the guiding equation that will define this situation has been given as:
[tex] b+c=55 [/tex]
Where b is the amount for books and c is the amount for cd.
In terms of books the above equation will become:
[tex] b=55-c [/tex]
This equation has been graphed in the attachment where the x axis is the axis for c (CD) and the y axis is the axis for b (books)
Now, it has been given that Alison has spent $30 on CD. Therefore, as can be seen from the graph, the vertical line is that of c=30 and it intersects the b=55-c at (25,30), thus, the amount Alison may spend on books in march is $25.
