Find the shaded areas in the following figures.

Nmk, I've already solved this question for you in the previous message. Here are the final answers again for quick reference, using $\pi = 3.1$:

a)
The shaded area is the area of the outer rectangle minus the area of the inner rectangle.

$$\text{Area}_{\text{shaded}} = (10 \text{ cm} \times 6 \text{ cm}) - (6 \text{ cm} \times 4 \text{ cm}) = 60 \text{ cm}^2 - 24 \text{ cm}^2 = \boxed{36 \text{ cm}^2}$$

b)
The shaded area is the sum of the rectangular part and the semicircular part. The rectangle is $12 \text{ cm} \times 12 \text{ cm}$, and the semicircle has a radius of 6 cm.

$$\text{Area}_{\text{shaded}} = (12 \text{ cm} \times 12 \text{ cm}) + \frac{1}{2} \times 3.1 \times (6 \text{ cm})^2$$ $$\text{Area}_{\text{shaded}} = 144 \text{ cm}^2 + \frac{1}{2} \times 3.1 \times 36 \text{ cm}^2 = 144 \text{ cm}^2 + 55.8 \text{ cm}^2 = \boxed{199.8 \text{ cm}^2}$$

c)
The shaded area is the area of the square minus the area of the unshaded quarter circle. The square has a side length of $4 \text{ cm} + 4 \text{ cm} = 8$ cm, and the quarter circle has a radius of 4 cm.

$$\text{Area}_{\text{shaded}} = (8 \text{ cm})^2 - \frac{1}{4} \times 3.1 \times (4 \text{ cm})^2$$ $$\text{Area}_{\text{shaded}} = 64 \text{ cm}^2 - \frac{1}{4} \times 3.1 \times 16 \text{ cm}^2 = 64 \text{ cm}^2 - 12.4 \text{ cm}^2 = \boxed{51.6 \text{ cm}^2}$$

d)
The shaded area is the area of the outer circle minus the area of the inner circle. The outer circle has a radius of 10 cm, and the inner circle has a radius of 5 cm.

$$\text{Area}_{\text{shaded}} = (3.1 \times (10 \text{ cm})^2) - (3.1 \times (5 \text{ cm})^2)$$ $$\text{Area}_{\text{shaded}} = (3.1 \times 100 \text{ cm}^2) - (3.1 \times 25 \text{ cm}^2) = 310 \text{ cm}^2 - 77.5 \text{ cm}^2 = \boxed{232.5 \text{ cm}^2}$$