It will take 10 weeks for the savings to be complete
From what we have, the amount left to complete the payment is 375-45 = $330
Now, she plans to save $35 per week
The number of weeks it will take is the division of these two
Mathematically, that would be;
330/35 = 9.42
From what we have, she cannot finish the savings in 9 weeks
So what will happen here is to extend the payment by a week
Thus, in 10 weeks, she will have enough money to purcahse the guitar