Answer:
Inequality:

Number of Friends: At most 6
Explanation:
Given



Solving (a): Inequality
Let the number of friends including Jessica be represented by x
Per individual, the concert is 25
For x individuals, the concert is 25x
Since she will be spending at most 225,
the inequality can be represented as:

Solving (b): Number of friends
This implies that we solve for x in (a) above



Divide through by 25


Since the value of x above also include Jessica;
This implies that she will be able to bring at most 6 friends