is this possible?

so is this possible, if so can someone please show me how? :)

i want a textbox that only takes numerical values. i want it to on a button press link to paypal with the value entered in the box as the quantity and the value per 1 being 1. once its paid for i want it to return to a thank you page and edit database to minus the number sold in paypal from a total number.

 

is this doable? sorry if in wrong place as new here and to asp.net
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