I have a Marexar CX zoom lens no.8407598 and am looking for an adaptor to fit it to a Canon EOS 1100D camera. What do I need?
That number is the serial number of the lens and isn't useful for identifying it by itself. Please see this question about mounting a similar lens to a Nikon camera: Which adapter do I need to mount a vintage Marexar-CX Lens to Nikon D3100?
The key point is that the lens itself comes in different mounts, and you'll need to identify which. Once you've done that, the adaptor you will need will be the one which matches that mount type to Canon EF mount.
Also, be aware that these are generally very low-quality lenses and it just might not be worth it.