Further to Stuart's response, to answer this question you need an understanding of VMC and the VFR cruising levels.
Outside controlled airspace ( ie in class G airspace) VMC is summarised in the graphic below - refer to the AIP. Note that the vertical distance below cloud for VMC is 1000'.
Now, since the forecast indicates OVC AC 8000/9000 you cannot maintain VMC above 7000'. This will limit your available cruise level to 7000' or lower.
But wait, there is more!.
When cruising at or above 5000' you are required to cruise at a VFR level outlined in the graphic below - refer to AIP.
On a heading of 090M, your available VFR cruise levels are limited 5500, 7500 or 9500.
At 9500 VMC cannot be maintained and is not an option given in the question
At 7500 VMC cannot be maintained as you cannot maintain 1000' vertical separation from the cloud base
At 5500 VMC can be maintained
In summary, the highest VFR cruise altitude available on this flight is 5500'