\( \frac{}{}+\frac{8}{21}=-\frac{4}{21} \)

To solve the equation \( \frac{}{}+\frac{8}{21}=-\frac{4}{21} \), we first need to isolate the fraction on the left. If we denote the empty fraction as \( x \), the equation becomes: \[ x + \frac{8}{21} = -\frac{4}{21} \] Subtract \( \frac{8}{21} \) from both sides: \[ x = -\frac{4}{21} - \frac{8}{21} \] Combining the fractions gives: \[ x = -\frac{(4 + 8)}{21} = -\frac{12}{21} \] Simplifying this, we factor out the greatest common divisor: \[ x = -\frac{4}{7} \] So, the solution is: \[ x = -\frac{4}{7} \] Feel free to reach out if you'd like to dive deeper into fraction operations or more algebraic concepts!