To determine the length of the car park as depicted in the blueprint (scale drawing), we first need to find the scale factor used by John. Since he used a scale factor of 1 inch : 15 feet, we can multiply the actual length of the car park by this ratio to get the length of the car park on the blueprint.
So, if the actual car park is 12 ft long, the length of the car park on the blueprint would be:
12 ft * 1/15 ft/inch = 8 inches
Therefore, the length of the car park as depicted in the blueprint is 8 inches.