Exercise 2 - solution

dry mass = 250 x (1 - 0.53) = 117.5 kg

At 10.5 percent: 117.5 / 0.895 = 131.3 kg
At 12.5 percent: 117.5 / 0.875 = 134.3 kg

Script lines:
print(f"{final_mass(250, 0.53, 0.105):.1f} kg")   # 131.3
print(f"{final_mass(250, 0.53, 0.125):.1f} kg")   # 134.3

The difference is about 3 kg out of 250 kg: a small weight difference, so the moisture target is mainly about storage safety and quality, not weight. (Assumes only water is lost.)