When 2 angles and a non included side of a triangle are equal to the corresponding angles and sides of another triangle, then the triangles are congruent. Looking at the triangles
Triangle BCD has 2 angles and a non included side
Triangle VTU has 2 angles and a non included side
The similar marks on the angles and sides shows that they are congruent. Thus, by AAS rule,
Triangle BCD is congruent to triangle VTU