Two angles are supplementary if the sum of their measures is 180 degrees. Given the two angles:
- \( m∠ACB = 4x \) degrees
- \( m∠BCD = (6x + 50) \) degrees
We can set up the equation as follows:
\[ 4x + (6x + 50) = 180 \]
Now, combine like terms:
\[ 4x + 6x + 50 = 180 \] \[ 10x + 50 = 180 \]
Next, subtract 50 from both sides:
\[ 10x = 130 \]
Now, divide by 10:
\[ x = 13 \]
Now that we have the value of \( x \), we can find the measure of angle \( ∠ACB \):
\[ m∠ACB = 4x = 4(13) = 52 \]
Thus, the measure of \( ∠ACB \) is:
\[ \boxed{52} \text{°} \]