Question 143924
Now we know that the amount of pure detergent in the 85% solution (0.85x) plus the amount of pure detergent in the 50% solution (0.50(10-x)) has to equal the amount of pure detergent in the final mixture (0.70)*10, so our eq to solve is:

0.85x+0.50(10-x)=0.70*10, so a=10

Hope this helps---ptaylor