To find an equivalent ratio of \( 4:x \) that is equivalent to the ratio \( 12:9 \), we can first simplify \( 12:9 \).
The greatest common divisor (GCD) of 12 and 9 is 3. Dividing both terms by 3, we get: \[ 12 \div 3 = 4 \quad \text{and} \quad 9 \div 3 = 3 \] So, the simplified ratio \( 12:9 \) is \( 4:3 \).
Now we can set \( 4:x \) equal to the simplified ratio \( 4:3 \): \[ \frac{4}{x} = \frac{4}{3} \]
To find \( x \), we can cross-multiply: \[ 4 \cdot 3 = 4 \cdot x \] This simplifies to: \[ 12 = 4x \] Now, divide both sides by 4: \[ x = \frac{12}{4} = 3 \]
The equivalent ratio of \( 4:x \) is therefore: \[ 4:3 \]
So, the answer is \( \mathbf{4:3} \).