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Also note that you can use "Я задумывался как повысить эффективность наших работников.". Key difference here is indefinite moment of time. If you point to moment of time ("Вчера вечером") - you must...

Also "работнинов" -> "работников".
And yes, it is correct.

(2) is perfect match. "прислушались" is good for this context.
(1)
"задумывался" is incorrect here. it is imperfect and implies repetative or indefinite action:
"Я часто задумывался о...", "Я...