Hello:
What is the formula or method used to determine the price to charge?
Also, the size of the images are shown as 10" x XX". Which is the width and which is the height?
there is no formula. just price it the way you want. it's not a height or width, the price starts at whatever is 10" because it can be either portrait or landscape.
Look around at some other photographers. I believe you will find your prices are on the high side for sn 8 inch print. Also, why only the one size for sale?
you will only see the price you pay.... if you changed default, it will only effect future things. you have to use the bulk edit to change what you have up.