Question 564784
The "percent solution" is the amount of minoxidil divided by the total volume. Let 'v' be the amount of 9% to add. Then we have (0.09*v+70*0.02)/(v+70)=0.07. This gives v=175. We can check the answer by making sure 2% of 70 plus 9% of 'v' is equal to 7% of 70+v.