\frac{w_1}{w_2}= \frac{A_2 -A_{avg}}{A_{avg}-A_1}= \frac{40-30}{30-25} =\frac{2}{1}: \frac{A}{B}
Now, we know that A is 111ml thus, B will be \frac{111}{2} or 55.5
To know more about mixture questions: https://gmatclub.com/forum/weighted-average-and-mixture-problems-on-the-gmat-206999.html