ANSWER
The correct choice is 50.
EXPLANATION
It was given that,
[tex] m \angle3 = 3x - 16[/tex]
and
[tex]m \angle4 = x + 84[/tex]
The two given angles are vertically opposite to each other.
Recall that, vertically opposite angles are equal.
This implies that:
[tex]3x - 16 = x + 84[/tex]
Group similar terms,
[tex]3x - x = 84 + 16[/tex]
[tex]2x = 100[/tex]
Divide both sides by 2
[tex]x = 50[/tex]
