She already has $8 so we will first subtract to see how much more money she needs.
57.50 - 8 = 49.50
So, Marianna needs $49.50 more. To find out how many weeks it will take her to get this amount we will divide.
49.50 ÷ 4.50 = 11
So, It will take Marianna 11 weeks to save enough money for her new tennis racket.
Hope I helped ya!!