Hi there!
[tex]\large\boxed{102^o}[/tex]
Using the triangle exterior angle theorem, we know that:
∠4 = the other two angles of the triangle combined (both are given)
Thus:
∠4 = 51 + 51 = 102°
Angle 4 is an outside angle.
An outside angle of a triangle is equal to the sum of the two opposite inside angles.
The two opposite inside angles to angle 4 are shown as 51 and 51
Angle 4 = 51 + 51
Angle 4 = 102 degrees.
