So... let's change the concentration percentage to decimal format. .. so 40% is just 4/100 or 0.4 and so on.

so... whatever "x" and "y" may be, we know the must add up to 6 liters.
and whatever 0.4x and 0.8y are, we also know, they must add up to a 3 of concentrated amount.
thus

solve for "x", to see how much of the 40% solution will be needed.
what about "y"? well, y = 6 - x.
Answer: 
Step-by-step explanation:
It is important to remember that an Exponential function has the following form:

Where “b” is
and
, "a" is a coefficient, "x" is the Independent variable and f(x) is the Dependent variable.
In this case, you have the following Exponential Function given in the exercise:

If the value of Dependent variable is -3, then:

So, you must substitute that value of "x" into the function:

And now you must evaluate:
1. According the Negative exponent rule:

Then:

2. Simplifying, you get:

I think the domain and range are infinite