Changing a prefixed unit to a base unit. By which conversion factor do we multiply $35 \mathrm{~m}$ to change it to km?

Step 1 ：Given a value of 35 meters, we need to convert it to kilometers.

Step 2 ：We know that 1 kilometer is equal to 1000 meters, so we need to divide the given value in meters by 1000 to get the value in kilometers.

Step 3 ：\(\text{meters} = 35\)

Step 4 ：\(\text{conversion_factor} = 1000\)

Step 5 ：\(\text{kilometers} = \frac{\text{meters}}{\text{conversion_factor}}\)

Step 6 ：\(\text{kilometers} = \frac{35}{1000}\)

Step 7 ：\(\text{kilometers} = 0.035\)

Step 8 ：\(\boxed{0.035\text{ km}}\)