A rectangular plot of land measures 120m by 80m. 1/3 of the land is used for maize, 25% for beans, and the rest is shared between tomatoes and cabbage in a 2:3 ratio respectively. Calculate the area a

The land measures 120 meters by 80 meters.

$$\text{Total Area} = 120\, \text{m} \times 80\, \text{m} = 9600\, \text{m}^2$$

Area for maize = $\frac{1}{3}$ of total area

$$\text{Area}_{\text{maize}} = \frac{1}{3} \times 9600\, \text{m}^2 = 3200\, \text{m}^2$$

Area for beans = 25% of total area

$$\text{Area}_{\text{beans}} = 0.25 \times 9600\, \text{m}^2 = 2400\, \text{m}^2$$

$$\text{Remaining Area} = \text{Total Area} - (\text{Area}_{\text{maize}} + \text{Area}_{\text{beans}})$$ $$\text{Remaining Area} = 9600\, \text{m}^2 - (3200\, \text{m}^2 + 2400\, \text{m}^2)$$ $$\text{Remaining Area} = 9600\, \text{m}^2 - 5600\, \text{m}^2 = 4000\, \text{m}^2$$

The remaining land is shared by tomatoes and cabbage in the ratio 2:3. The total ratio parts are $2+3=5$.
The fraction of land for cabbage is $\frac{3}{5}$.

$$\text{Area}_{\text{cabbage}} = \frac{3}{5} \times \text{Remaining Area}$$ $$\text{Area}_{\text{cabbage}} = \frac{3}{5} \times 4000\, \text{m}^2 = 2400\, \text{m}^2$$

The total area of the land allocated for cabbage is $\boxed{\text{2400 m}^2}$.

From part a), the area for maize is $3200\, \text{m}^2$.
Each square meter of maize land produces 5 kg of maize.

$$\text{Estimated Maize Yield} = 3200\, \text{m}^2 \times 5\, \text{kg/m}^2 = 16000\, \text{kg}$$

The maize yield decreased by 15%.

$$\text{Actual Maize Yield} = \text{Estimated Maize Yield} \times (1 - 0.15)$$ $$\text{Actual Maize Yield} = 16000\, \text{kg} \times 0.85$$ $$\text{Actual Maize Yield} = 13600\, \text{kg}$$

The actual yield of maize is $\boxed{\text{13600 kg}}$.

The farm is located 30 meters above sea level.

$$\text{Initial Altitude} = 30\, \text{m}$$

The water levels rose by 12 meters. This means the new effective sea level is 12 meters higher than the original sea level.
To find the farm land's altitude relative to the new sea level, subtract the water level rise from the initial altitude.

$$\text{Final Altitude} = \text{Initial Altitude} - \text{Water Level Rise}$$ $$\text{Final Altitude} = 30\, \text{m} - 12\, \text{m} = 18\, \text{m}$$

The final altitude of the farm land relative to sea level after the flood is $\boxed{\text{18 m}}$.