Problem with basic variable math

Questions & Suggestions
2

While you're waiting, I would be tempted to paste this kind of thing into an Execute JavaScript for Automation action:

(() => {
    'use strict';

    // standardAdditions :: () -> Application
    const standardAdditions = () =>
        Object.assign(Application.currentApplication(), {
            includeStandardAdditions: true
        });

    const v = standardAdditions().theClipboard();
    return isNaN(v) ? (
        'NaN'
    ) : parseInt(v, 10) + 10;

})();