Name the instruments that are used to measure the following. (i) Length of a soccer field (ii) Things that are not straight (iii) Distance that you have travelled in a vehicle

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4. Convert 15 mm to m. Step 1: Recall the conversion factor from millimeters to centimeters. $1 cm = 10 mm \implies 1 mm = \frac{1}{10} \text{ cm}$ Step 2: Convert millimeters to centimeters. $15 mm = 15 \times \frac{1}{10} cm = 1.5 \text{ cm}$ Step 3: Recall the conversion factor from centimeters to meters. $1 m = 100 cm \implies 1 cm = \frac{1}{100} \text{ m}$ Step 4: Convert centimeters to meters. $1.5 cm = 1.5 \times \frac{1}{100} m = 0.015 \text{ m}$ The conversion is $\boxed{0.015 m}$.

5. Convert 28 cm to km. Step 1: Recall the conversion factor from centimeters to meters. $1 m = 100 cm \implies 1 cm = \frac{1}{100} \text{ m}$ Step 2: Convert centimeters to meters. $28 cm = 28 \times \frac{1}{100} m = 0.28 \text{ m}$ Step 3: Recall the conversion factor from meters to kilometers. $1 km = 1000 m \implies 1 m = \frac{1}{1000} \text{ km}$ Step 4: Convert meters to kilometers. $0.28 m = 0.28 \times \frac{1}{1000} km = 0.00028 \text{ km}$ The conversion is $\boxed{0.00028 km}$.

6. Convert 12 km to mm. Step 1: Recall the conversion factor from kilometers to meters. $1 km = 1000 \text{ m}$ Step 2: Convert kilometers to meters. $12 km = 12 \times 1000 m = 12000 \text{ m}$ Step 3: Recall the conversion factor from meters to centimeters. $1 m = 100 \text{ cm}$ Step 4: Convert meters to centimeters. $12000 m = 12000 \times 100 cm = 1200000 \text{ cm}$ Step 5: Recall the conversion factor from centimeters to millimeters. $1 cm = 10 \text{ mm}$ Step 6: Convert centimeters to millimeters. $1200000 cm = 1200000 \times 10 mm = 12000000 \text{ mm}$ The conversion is $\boxed{12000000 mm}$.