A rectangular stadium has a length of 20m and a width of 12m. It is surrounded by a uniform margin of 3m on all sides. Calculate the total area of the stadium including the margins and the area of the

The total width A is the sum of the left margin, the width of the ground, and the right margin.

$$A = 3 \text{ m} + 20 \text{ m} + 5 \text{ m}$$ $$A = 28 \text{ m}$$

The total height B is the sum of the top margin, the height of the ground, and the bottom margin.

$$B = 3 \text{ m} + 12 \text{ m} + 5 \text{ m}$$ $$B = 20 \text{ m}$$

The values for A and B are $\boxed{A = 28 \text{ m}, B = 20 \text{ m}}$.

2. Calculate the area that will be tilled
Assuming "tilled" refers to the area of the stadium excluding the ground (e.g., for tiling stands or walkways).

The area of the stadium is given by the formula $A_{stadium} = \text{length} \times \text{width}$.

$$A_{stadium} = A \times B$$ $$A_{stadium} = 28 \text{ m} \times 20 \text{ m}$$ $$A_{stadium} = 560 \text{ m}^2$$

The area of the ground is given by the formula $A_{ground} = \text{length} \times \text{width}$.

$$A_{ground} = 20 \text{ m} \times 12 \text{ m}$$ $$A_{ground} = 240 \text{ m}^2$$

This is the area of the stadium minus the area of the ground.

$$A_{tilled} = A_{stadium} - A_{ground}$$ $$A_{tilled} = 560 \text{ m}^2 - 240 \text{ m}^2$$ $$A_{tilled} = 320 \text{ m}^2$$

The area that will be tilled is $\boxed{320 \text{ m}^2}$.