B
the other options all have a set price, the answers in b could all change price from month to month
Step-by-step explanation:
If there were 7 items, the number of ways to choose 7 out of the 7 items is only 1 way, which is to get all of them.
=> 7C7 = 1.
Rate of change =30
slope intercept form: y=30x+b
