Printing paper sizes

I am trying to print a photograph - i would like to print it on to my 5x7 glossy paper.

I have select 5x7 glossy paper on my brand new printer.

However when I try to find a 5x7 on my brand new Window 10 pc there is no option. It does not exist!!

I have selected 'Letter' in printer properties, as suggested by a thread I found, but there is no option to custom the paper size.

I'm suck. Can any one help? 

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