Alison set aside $55 each month to spend on books and cd .if she spends c dollar on cds given a month she may spend b dollar on book where c +b =55. graph the equation and use the graph to estimate the amount alison may spend on books in march if she spends 30 on cds

For this case we have the following equation:
 c + b = 55
 Where,
 c: number of CDs
 b: number of books
 For c = 30 we have:
 30 + b = 55
 From here, we clear the value of b.
 We have then:
 b = 55-30
 b = 25
 Note: observe in the graph that when the value of c is 30, the value of b is 25.
 
 the amount Alison may spend on books in March if she spends 30 on CDs is:
 b = 25
 See attached image.

The answer to your question is i think 7

The correct answer would be "convenience"