To find the missing number that makes the fractions equal, you can cross-multiply.
Starting with the equation:
\[ \frac{4}{6} = \frac{x}{42} \]
Cross-multiply:
\[ 4 \times 42 = 6 \times x \] \[ 168 = 6x \]
Now, divide both sides by 6 to solve for \(x\):
\[ x = \frac{168}{6} = 28 \]
Therefore, the missing number is 28.
So the complete equation is:
\[ \frac{4}{6} = \frac{28}{42} \]