.
How much pure acid should be mixed with 3 gallons of a 20% acid solution in
order to get a 60% acid solution?

3 gallons

Step-by-step explanation:

Let

x ----> the amount of pure acid (100% solution) in gallons

Remember that

we know that

solve for x

therefore

3 gallons of pure acid should be mixed with 3 gallons of a 20% acid solution in  order to get a 60% acid solution

x² + 3x + 7 = 0       [ax² + bx + c]

a = 1

b = 3

c = 7

quadratic formula:

    (+/- is this ±)

plug in the numbers into the variables

your answer is a