It would have been plus seven if possible, however the maximum is the number of valence electron of sulfur to be donated, so that is clearly +6 (six).

i.e. 2 +2x -16=0

=>x =7, but for sulphur x cannot be greater than 6... so this means , there is a peroxy linkage in the given compound...

and we know that , peroxy oxygen have oxdn. no. -1

whenever there is peroxy linkage , sulphur is always in its highest oxdn. state i.e. +6

so here, oxdn. state of sulphur is +6

now u can also find the no. of peroxy linkages..

i.e. 2+2(6) +n(-1) -(n-8)(-2) = 0

so , here n = 2. so we have two peroxy oxygens and one peroxy linkage.