Two angles are supplementary when the sum of their measures is 180 degrees. Therefore, we can set up the following equation:
\[ m∠ACB + m∠BCD = 180° \]
Substituting the measures of the angles:
\[ 4x + (6x + 50) = 180 \]
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:
\[ m∠ACB = 52° \]