The expression can be simplified as:
b-8
Here is the equation:

You need to find f(3). To do that, substitute all the x's with 3:

The first thing you need to do is multiply 4 by 3. Multiply:

Here is your new equation:

To get your answer, you need to add 12 and 1. Add:

That means:

<em>If you have any questions, feel free to ask in the comments! :)</em>
Where is it? Don’t see it so uh
"Bucket method"
.. (4)*(14%) + (x)*(8%) = (4 +x)*(10%) . . . . . liters and % are in each "bucket"
.. 56 +8x = 40 +10x . . . . . multiply by 100, eliminate parentheses
.. 16 = 2x . . . . . . . . . . . . . . add -40-8x, then divide by 2
.. 8 = x
8 liters of 8% lemonade should be added to make the mixture 10% lemon juice.