\( \left. \begin{array} { l }{ 25 \times 3 \times 4 = 3 \times \_ \times } \\ { = 3 \times } \\ { = } \end{array} \right. \)

To solve the equation \( 25 \times 3 \times 4 = 3 \times \_ \times \), we first calculate the left side: \[ 25 \times 3 = 75 \] \[ 75 \times 4 = 300 \] So, we have: \[ 25 \times 3 \times 4 = 300 \] Now, we set the right side equal to 300: \[ 300 = 3 \times \_ \times \] To find the value of \( \_ \), we can divide both sides by 3: \[ \_ \times = \frac{300}{3} = 100 \] Thus, we can fill in the blank: \[ \_ = 100 \] So the complete equation is: \[ 25 \times 3 \times 4 = 3 \times 100 \] And both sides equal 300. Therefore, the answer is: \[ \boxed{100} \]