use a ruler. The method used then depends on the way the scale is written. For a measurement-based scale where one or more units (cm or inch) represent a given distance, eg 2 cm to 5 km, or 1 inch ...

What you need: ruler, protractor, pencil and paper. Use these to construct a triangle when you know the length of 1 side and the 2 angles at each end of it. In this case use the length 8 cm ...