Answer: It will take 15 weeks for Cyndi and her sister to have the same amount of money.
Explanation:
Given: Cyndi has $55. Her sister has $115.
Cyndi saves $10 per week. Her sister saves $6 per week.
Let x= Number of weeks.
Total amount of money Cyndi has = 55+10x (i)
Total amount of money sister has = 115+6x (ii)
From (i) and (ii) , we get

Hence, it will take 15 weeks for Cyndi and her sister to have the same amount of money.