Question 973905
x=ounces of 20%
12-x=ounces of 50%

0.20x + 0.50(12-x) =0.3acid*12ounces

0.20x + 6-0.50x =3.6 acid ounces

-0.30x=-2.4; divide both sides by -0.30
x=8 ounces ;;  20%  ;;  8*0.20=1.6

12-x=4 ounces ;;50%  ;; 4*0.50=2

Sum is 3.6 acid-ounces