Two angles are supplementary if the sum of their measures equals 180 degrees.
Given:
- \( m∠QRS = (x + 40)° \)
- \( m∠SRT = x° \)
Setting up the equation for supplementary angles, we have:
\[ (x + 40) + x = 180 \]
Combining like terms:
\[ 2x + 40 = 180 \]
Subtracting 40 from both sides:
\[ 2x = 140 \]
Dividing by 2:
\[ x = 70 \]
Now, we can find the measure of \( m∠QRS \):
\[ m∠QRS = x + 40 = 70 + 40 = 110° \]
Thus, the measure of \( ∠QRS \) is:
110 degrees.