I want to multiply entered number with $10 in donation checkout form

When a user enters a number on the checkout page, I want to multiply that number by 10, and the result should be the total amount in the checkout form. This calculation can either take place on the checkout page or on a different page. Or maybe I can use a digital product, setting 10 as the default quantity, so the value automatically multiplies by 10 and outputs the required result?
Any guidance will be highly appreciated.

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