I go for a
Farman F 40
tapered tailbooms suggest a pusher, the rudder matches Farman and the tail-tombstone indicate type 40.
But it could be also a derive, probably not a belgian but maybe a russian, though there is no Tereshenko-logo visible
.
We didn't had much of them in the challenges - so there is a whole range possible...
Cheers
Aquilius