A shooting gallery here- killing ghuls with arrows- bonuses for doing so inside the time limit and with fewer than five arrows. If you've accomplisehd the latter you've almost certaily accomplished eeh former, which makes things easy. As you might guess, the key here is to shoot, not the ghuls themselvrs, but grog barrels conveniently lining the path. Start immediately with the one dead ahead.
Wait a moment for the ghuls to regroup, then shoot the barrel just under your previous target.
That should get you to between 35-40 ghul deaths right there, so just shoot a third barrel anywhere near another ghul swarm to complete the mission.
If you're having trouble, note the ghul stream here is not infinite- If you have a choice of barrels it's better to use the ones higher on the path- there may not be any ghuls there later, but every ghul will have to pass by the lowermost barrel.