Two lines intersect at a point. the vertical angles formed are supplementary.

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