Given that "Triangles QVS and RTS are similar".
We know that ratio of corresponding sides in similar triangles are equal so we will use that property here.
Possible ratio of corresponding sides are:
QV/RT=VS/TS=QS/RS
Now plug the given values from the picture.
26/10=x/28=QS/RS
or 26/10=x/28
or 26*28=10*x (cross multiplication)
or 728=10*x
or 728/10= x
or 72.8=x
Hence final answer is side VS=x=72.8