we know that
Vertical angles are a pair of opposite and congruent angles formed by intersecting lines.
so
Let
x1---------> angle vertical 1
x2---------> angle vertical 2
x1=x2 ------> equation 1
in this problem
if the vertical angles formed are supplementary
that means that
x1+x2=180 ------> equation 2
substitute equation 1 in equation 2
x1+x1=180
2x1=180
x1=180/2
x1=90 degrees
therefore
the answer is
The vertical angles are right angles