Answer:
the measure of ∠4 is 60°
Explanation:
Two angles are Vertical angles when they are opposite to each other and are congruent.
As per the statement:
If m∠4 = (3x)° and m∠8 = (x + 40)°
Since, angles 4 and 8 being vertical.
then by definition we have;

Substitute the given values we have;

Subtract x from both sides we have;

Divide both sides by 2 we have;
x = 20
Substitute the value of x in m∠4 = (3x)°
then;
m∠4 = (3(20))° = 60°
Therefore, the measure of ∠4 is 60°