Had another study of the photo. Updated.
The big ring is about 10mm smaller than the crank length, which might make it 160 mm, x 2 = 320, x 3.1415 = 1005, divided by 25.4 = 39.5”, x 0.5 = 79 teeth.
The sprocket looks a 28.
There’s another ring behind, which might be 12 teeth smaller. 67.
So a ‘low’ gear of 55”. Not rediculous if the roads have no hills.