Place the compasses on the point and draw an arc which crosses the line once on either side of the point. Place the compasses on the left-hand point of intersection, set them to just over halfway ...
The sketch is given using the scale 1 cm = 1 mile. Draw a parallel line that is 1.5 cm from the line EF. All points to the right of this line are at least 1 ½ miles away from the marshland.