It looks like the marathons are rated to 70 PSI, but as so much of the riders weight is right over the rear axle on these bikes I like to run the rear pretty hard so the bike rolls decently, I've found that 85-90 PSI seems to still be comfy, but I can cover ground decently.
The tires I have coming are rated to 100 PSI, the
KENDA KWEST 16X1.5 K193-2 black bike 100 PSI, here is a link,
https://www.ebay.com/itm/372586676997