If she took $20 out of her savings account, given the information, she could easily have no money remaining now. Given this, we'll assume the current value of her account is the minimum it can be. Now you just need to find how many times her withdrawal can factor into the original amount, $250. Therefore, t=250/20= 12.5. Since it's asking for a number of weeks, the answer can't be a decimal, so your final answer is 12 weeks.
