。
There were several pictures hanging on the wall.
Literal
Wall [on-には] paintings [subject-が] some hung was.
かけてあった is the past tense of かけてある — the ~てある construction marks the result of a deliberate action by someone unstated: 'someone hung those pictures, and they remained hung.' Distinct from ~ている, which would simply describe an ongoing state. 何枚か uses 何 + counter 枚 + か for an indefinite 'some number of (flat things).'