To be able to calculate that, one would have to know the elevation of the satellite at your location. Your profile says you're in Iran, so I assumed Tehran to get a rough estimate, where Asiasat 7 has an Elevation angle of 20.38°.
If you're 24 m from an 8 meter high wall, the top of the wall will be at 18.43° from your location (ground level). So you should be able to see the satellite. Plus, you get some channels, so that's another hint.
Trees in the way may let some signal through, walls generally completely block it (not absolutely true; I once received Astra 1 analogue through a brick wall, but stuff like that is unusual).