Exercise: Focal length and angle of view

For this exercise I used the tripod to keep the camera in fixed position.
Picture 1 was taken at: 4sec, f5,ISO 100, 10mm focal length
Picture 2 was taken at: 6sec,f5.6, ISO 100, 20mm
Picture 3 was taken at: 2.5 sec, f5, ISO100, 18mm
Picture 4 was taken at: 5sec,f5.6,ISO100,55mm

I was asked to print the picture to size A4 and measure the distance from the camera to when print and object look the same size.
In picture 1 the print almost touched the camera aroun 10cm away
In picture 2 the print was around 20-30cm away from the camera
Change of lense
In picture 3 the print was 20 to 30 cm away, the focal length was slightly different
In picture 4 the print was at armth length almost touching the bookcase, perhaps 60-70 cm away