I think you either add all of the sides or multiply but i think you multiply
First, you would add 9x to both sides so that you get:
x^2 + 9x + 20 = 0.
Then, you want to factor. You want coefficients of x that add to 9 and have the constants add to 20:
(x + 5) * (x + 4) = 0
The answer is (C).
Acid is 0.2*5 = 5* 1/5 = 1 liter. We should multiple mass and concentration (in this conditions). So, 1 liter.
so it went down from 25 to 18, so 25 - 18 = 7.
if we take 25 to be the 100%, what is 7 off of it in percentage?