Supplementary angles add up to 180°. Therefore, we can set up the equation:
\[ m∠D + m∠E = 180° \]
Substituting the expressions for the angles:
\[ (4x + 8) + (x + 17) = 180 \]
Combining like terms:
\[ 5x + 25 = 180 \]
Next, we can isolate \(x\) by subtracting 25 from both sides:
\[ 5x = 155 \]
Now, divide by 5:
\[ x = 31 \]
Now we can find the measure of ∠D:
\[ m∠D = 4x + 8 = 4(31) + 8 = 124 + 8 = 132° \]
Since ∠F is a vertical angle with ∠D, they are equal in measure. Thus:
\[ m∠F = m∠D = 132° \]
The final answer is:
132°