Theory
A scale drawing is an accurate drawing where every length has been enlarged or reduced by the same scale.
A map scale tells you how a distance on the map compares with a real distance.
For example, 1 cm represents 2 km means every 1 cm on the map is 2 km in real life.
To find a real distance, multiply the map distance by the scale.
To find a map distance, divide the real distance by the scale.
A ratio scale such as 1 : 50 means 1 unit on the drawing represents 50 of the same unit in real life.
Always check units. If the scale mixes cm and km, keep the meaning clear rather than treating the numbers as the same unit.
Scale drawings often combine with bearings: draw the direction accurately, then use the scale for distance.