A simple magnifier of focal length 5cm and a compound microscope (tube length 20cm) having an objective of focal length 1cm and an eyepiece of focal length 5cm are both adjusted so that their final images are at infinity. Taking the least distance of distinct vision D=25cm, what is the ratio of the magnifying power of the compound microscope to that of the simple magnifier?
a) 16.7
b) 24
c) 20
d) 25