Write in kilograms and grams: 3380g, 7423g, 5.76kg, 12.53kg, 5.76kg. The lightness or heaviness of somebody or thing is and the (3).

$$
12.53 \text{ kg} = 12 \text{ kg} + 0.53 \text{ kg}
$$

$$
0.53 \text{ kg} = 0.53 \times 1000 \text{ g} = 530 \text{ g}
$$

$$
\boxed{\text{12 kg 530 g}}
$$

$$
5.76 \text{ kg} = 5 \text{ kg} + 0.76 \text{ kg}
$$

$$
0.76 \text{ kg} = 0.76 \times 1000 \text{ g} = 760 \text{ g}
$$

$$
\boxed{\text{5 kg 760 g}}
$$

$$
3380 \text{ g} = 3000 \text{ g} + 380 \text{ g}
$$

$$
3000 \text{ g} = 3 \text{ kg}
$$

$$
\boxed{\text{3 kg 380 g}}
$$

$$
7423 \text{ g} = 7000 \text{ g} + 423 \text{ g}
$$

$$
7000 \text{ g} = 7 \text{ kg}
$$

$$
\boxed{\text{7 kg 423 g}}
$$

$$
\text{Total beans bought} = 200 \text{ bags} \times 50 \text{ kg/bag} = 10000 \text{ kg}
$$

$$
\text{Beans for children} = 5 \text{ bags} \times 50 \text{ kg/bag} = 250 \text{ kg}
$$

$$
\text{Total beans used} = 5000 \text{ kg} + 250 \text{ kg} = 5250 \text{ kg}
$$

$$
\text{Beans left} = 10000 \text{ kg} - 5250 \text{ kg} = 4750 \text{ kg}
$$
$$
\boxed{\text{4750 kg}}
$$

$$
\text{Average Speed} = \frac{\text{Distance}}{\text{Time}}
$$

$$
\text{Average Speed} = \frac{28 \text{ km}}{4 \text{ hours}}
$$

$$
\text{Average Speed} = 7 \text{ km/h}
$$
$$
\boxed{\text{7 km/h}}
$$

$$
\text{Average Speed} = \frac{\text{Distance}}{\text{Time}}
$$

$$
\text{Average Speed} = \frac{270 \text{ km}}{3 \text{ hours}}
$$

$$
\text{Average Speed} = 90 \text{ km/h}
$$
$$
\boxed{\text{90 km/h}}
$$