First 1/5 is equivalent to 20% so to get 20% of both of them multiply by .2. so 400×.2=80 and 90×.2=18
So you have x^3 - 4x = 0. What you can do is pull out an x from both x^3 and - 4x so it looks like this:

Then you can find a number that makes the part inside the parentheses turn into zero. For beginners, it may be easier to write it out seperately and solve for x.

We need to solve for x, so the first step is to add 4 to both sides, so we get something like this:

Then, we can square root both sides to get rid of the power on the x, so it looks like this:

Now, every square root has two answers, a positive and a negative. If we look at the bottom example:


We can see that both -2 and 2 to the power of two will equal to 4.
So finally, we get:

These are the other 'Zero's for the original function. If you are not sure of what a 'Zero' is, it is where the function crosses over the x-axis on a graph.
Use substitution.
anywhere you see "a" , than you would plug in b + 2 in for it so....
(b - (b + 2)^4
now take the negative sign and distribute it "+"
so b - b is 0, than 0 - (-2) is -2.
so what is (-2)^4 ????? it would become positive 16
There are several important information's already given in the question. Based on those information's the answer to the question can be easily deduced.
Number of cups of Oatmeal
required by Aunt Bess for making 6 dozen cookies = 3
Then
Number of cups of oatmeal
required by Aunt Bess for making 1 dozen cookies = (3/6)
= 1/2
So
Number of cups of oatmeal
required by Aunt Bess for making 18 dozen cookies = (1/2) * 18
= 9 cups
So Aunt Bess will require 9 cups of oatmeal for baking 18 dozen cookies. I hope the procedure is clear enough for you to undestand.