Question

Triangles QVS and RTS are similar. Find side VS.

Answer 1

The triangles shown, QVS and RTS, have two pairs of congruent angles. That means the triangles are similar.
Similar triangles have proportional corresponding side lengths.

Answer 2

Sides QV and RT are corresponding.
Sides VS and TS are corresponding.
The ratio of QV to RT is equal to the ratio of VS to TS.
Set up a proportion. Only one of those 4 sides is an unknown, so you can solve the proportion for that unknown.