Answer:
The answer to your question is 14.5 weeks
Step-by-step explanation:
Data
Total cost = C = $87
money earned = m = $6
Number of weeks to have the money = w = ?
Process
1.- Write an equation that represents the situation
      Weeks = Total cost / Money earned
       w = C/m
2.- Substitute the values
       w = 87 / 6
3.- Result
       w = 14.5
4.- Conclusion
Niki will last 14.5 weeks to have enough money to buy a dog bed.