The conversion factor for kilometre to metre is 1000.
When we convert a bigger unit (km) to a smaller unit (m), we multiply.

Therefore, 1 km = $1\times 1000$ = 1000 m

'Litre' is the standard unit of capacity.

Measuring tape is used to measure length. For example, the length of a cloth. Compass shows direction. Measuring Can is used to measure the volume of a liquid.

The balance scale is the instrument used for weighing an object.

If we observe the picture, the pencil on the scale is starting at 1 cm. Ideally, it should start from zero. So, subtract 1 cm from 6 cm.

i.e Length of the pencil = 6 cm - 1 cm 

= 5 cm

We need to convert 300 m to km. To convert a smaller unit (m) to a bigger unit (km), we need to divide by the conversion factor.

We know that 1000 m = 1 km

$\therefore$ 300 m = $\frac{300}{1000}$ = 0.300 km.

Hence, 20 km + 0.300 km = 20.300 km = 20.3 km

We know that

1 Litre = 1000 mL

$\therefore$ 1000 mL = 350 mL + _____ mL

$\Rightarrow$ 1000 mL - 350 mL =  _____ mL
                                     = 650 mL
$\therefore$ 1000 mL = 350 mL + 650 mL

When we convert a larger unit (km) to a smaller unit (m), we multiply the given measure by the conversion factor.

Since 1 km = 1000 m, we multiply 3 by 3000 to convert 3 kms into metres.

i.e., 3km = 3 x 1000 m = 3000 m

To convert metres into centimetres, we multiply the given measure by 100.

i.e., 3000 m = 3000 x 100 cm = 300000 cm

Thus, Raju travels a total of 300000 cm everyday.

Since the units are same, the values can be easily subtracted 

20 mg - 1 mg = 19 mg

We know that spoon is a small object which can hold very little quantity of liquid. 

Here, millimetre (mm) and centimetre (cm) are units of length.

'Litre' is used to measure a large quantity of liquid.

Therefore, milk in a spoon is approximately 5 mL.

Initial position of the ant = 2 cm

Ant goes  3 cm forward = 2 cm + 3 cm = 5 cm

Ant goes 2 cm backward = 5 cm - 2 cm = 3 cm

Finally, the ant goes 5 cm forward = 3 cm + 5 cm = 8 cm
$\therefore$ The final position of the ant is 8 cm