Answer: 9 more breaths.
Since Wendy has already blown 1/4 of the balloon, you only need to find the remaining 3/4 of the air needed to fill the balloon. As the problem said, it said that Wendy took 3 full breaths to blow 1/4 of it. Multiply 3 (amount of breaths for the balloon to be filled 1/4 of the way) by 3 (3x3) Now you can tell that for the balloon to be filled 3/4 for the width she needs, it will require 9 more full breaths. Hope that helped!