Question

If m∠4 = (3x)° and m∠8 = (x + 40)°, what is the measure of ∠4?

∠4 and ∠8 are vertical.

Answer 1

If they are vertical, there magnitude would be equal.
3x = x + 40
3x - x = 40
x = 40/2
x = 20

So, m<4 = 3(20) = 60

Hope this helps!