0.25/ х = 0.5 / 8.4

To solve the equation \( \frac{0.25}{x} = \frac{0.5}{8.4} \), follow these steps:

1. Start by simplifying the right side of the equation: \[ \frac{0.5}{8.4} = \frac{5}{84} \quad \text{(since } 0.5 = \frac{5}{10} \text{ and } 8.4 = \frac{84}{10}\text{)} \] So, we can rewrite the equation as: \[ \frac{0.25}{x} = \frac{5}{84} \]

2. Cross-multiply: \[ 0.25 \cdot 84 = 5 \cdot x \]

3. Calculate \( 0.25 \cdot 84 \): \[ 0.25 \cdot 84 = 21 \]

4. Now the equation is: \[ 21 = 5x \]

5. Solve for \( x \): \[ x = \frac{21}{5} = 4.2 \]

Thus, the solution is: \[ x = 4.2 \]