To factor the expression \( \frac{21x}{2} + \frac{3x}{2} \), we can first combine the terms:
\[ \frac{21x}{2} + \frac{3x}{2} = \frac{21x + 3x}{2} = \frac{24x}{2} \]
Now, simplify \( \frac{24x}{2} \):
\[ \frac{24x}{2} = 12x \]
Now, to factor \( 12x \), we can express it as:
\[ 12x = 12 \cdot x \]
This is a simple factorization. If you wanted to break it down further, you could factor \( 12 \) as \( 6 \cdot 2 \), giving:
\[ 12x = 6 \cdot 2 \cdot x \]
So the original expression factors down to \( 12x \), or you could write it as:
\[ 12x = 2 \cdot 6x \]
In conclusion, the fully factored form of the original expression is \( 12x \).