A semitractor and trailer combination which is known to be 1

A semitractor and trailer combination which is known to be 18m long measures 11.3mm long on a vertical aerial photo. what is the scale of the photo at the elevation of the semi?

Solution

the scale is the ratio of original length to  the measure on vertical aerial photo

= 18m/11.3mm

= 18/11.3x10^-3

= 1.59292 x 10^3