What is proper tire pressure for most passenger cars?

I stop at quick lube for oil change- they say air pressure it too high… Maybe 35 -38 pounds. They lower it to 30.

Then I look on the tire and it says max press- 51 pounds!
What is it supposed to be?
Honda CRV…
Added (1). Okay- thanks for all the info. I got it now.
30 on the Honda…
On the old Volvo V70 its 32 front and 30 rear up to 500# weight of cargo and passengers.
And 38 all the way around for 500-1000#
Thats all cold tire pressure.

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