What is the length of the river if on the map its length is 6 centimeters 3 millimeters, the scale of the map is 1: 1000000?

First, you should convert the value of the length of the river on the map to centimeters.
Since 1 cm is 10 mm, we get:
6 cm 3 mm = 6 + 3/10 = 6 + 0.3 = 6.3 cm.
We find the length of the river on the ground in centimeters.
To do this, multiply the length of the segment by the map scale.
Will be:
6.3 * 1,000,000 = 6,300,000 cm.
We translate the length of the river into kilometers.
Since 1 km – 1000 m, and 1 meter – 100 cm, we get:
6300000 / (1000 * 100) = 6300000/100000 = 63 km.
Answer: the length of the river is 63 km.