3125 is radical expression that is an irrational number.

To find the means of a proportion, you can cross-multiply and then solve for the variable. Let's see:

\[ \frac{15}{2} = \frac{1}{4}x \]

Cross-multiply:

\[ 15 \times 4 = 2 \times x \]

\[ 60 = 2x \]

Now, solve for \( x \):

\[ x = \frac{60}{2} \]

\[ x = 30 \]

So, the means are 30 and 2. The correct option is not provided in the choices you've given. It seems like there might be a mistake in the options or the question.

8.12131415… is an irrational number.

-3 value is a solution to the inequality 9 - y >12.

9 - y >12
9 -12 > y
-3 > y

The simplified algebraic expression is C. 3x^2 - 6.
First, distribute x to simplify x(2x - 4): 2x^2 - 4x.
Then, subtract 6 from the result to get the final expression 3x^2 - 6.