The first thing we must do for this case is to define variables.
 We have then: 
 x: number of packages 
 y: amount of money the student earns per day 
 The equation modeling the problem is given by: 
 
 
 
 So, in order to earn $ 200 we have: 
 
 
 
 From here, we clear the value of x. 
 We have then: 
 
 
 
 
 
 
 
 
 
 
 
 
 Answer: 
 she must make 30 deliveries each day to earn 200 $ a day