Painstakingly count the number of teeth on each gear. For each set of meshing gears the ratio will be (output number of teeth / input number of teeth) which will give you some ratio as to one eg for first this maybe 3.2:1
For each gear (1st, 2nd, etc, except 4th) the drive will pass through multiple gear sets. To find the equivalent of a number of meshing gears, multiple the ratio of each set together.
Unless of course someone can identify the gear sets that are in there.