Number of bridge oxygen atoms in a silicate mineral

Question

Total number of oxygen atom(s) which act(s) as bridge between any two silicon atoms in a mineral with composition $\ce{MM’Si3O_x}$ $(\ce{M}$ is the divalent metal ion and $\ce{M’}$ is the tetravalent metal ion).

This is the question I have been stuck on. I do not understand how to approach it. Are we supposed to used the concepts of silicates? Like sheet silicate, chain silicate etc. or interstitial salts concepts?

Also, I don’t know whether it is possible to draw the structure as $x$ is a variable. Any hint would be appreciated.

P.S. Answer given is 3.

Answer 1

I am answering it to let others know that I have got the satisfactory answer, thanks to andselisk.

Since $\ce{M}$ is divalent and $\ce{M’}$ tetravalent, they exist as $\ce{\overset{2+}{M}}$ and $\ce{\overset{4+}{M’}},$ respectively. The anionic part is $\ce{[\overset{+4}{Si}_3\overset{-2}{O}_x]^6-},$ and taking oxidation numbers into consideration, $x = 9.$ $\ce{[Si3O9]^6-}$ moiety implies cyclic metasilicates:

There are three bridging oxygen atoms per ring or per formula unit. A real life example for the mineral from the problem could be benitoite $\ce{BaTiSi3O9}$.