We have an SFDC custom field (a number value) called "webinars registered". We have a Marketo form that people use to register for our webinars. Whenever somebody registers for our webinar, we want the "webinars registered" field in SFDC to increment +1 (e.g. if somebody registers for their first webinar, the "webinars registered" field would be 1; if somebody registers for their third webinar, it'd be 3, etc.).
Is there a way to rig up either Marketo or SFDC to do this?