It is plausible.
Kai came along with the concern that he may not meet the weekly quota.
His life was on the line.
After all, three thousand mana ores in a week aren't exactly a low number. He already made the calculations. Amassing that amount would be impossible with the current situation regarding the safe clouds, locked down by their rulers, and the current restrictions that are in place.
But with the new assigned clouds, it's possible.
Kai could see the light at the end of the tunnel.
Not to mention, gathering the mana ores is easier in Fire Swamp than in the other clouds.
Under the murky water, there are several boulders that contain mana ores in them, making mining the mana ores easier because of this. Much easier compared to mining them in a cave or underground.
Around this particular area, Kai and Matilda could find six of these boulders.
It took a moment for them to crack them open, and they continued on searching for more.
