3. The Pandora planet was attacked by 5400 flying dragons and 1800 ground tigers, and the mecha warriors fought hard. There are a total of 210 mecha warriors on Pandora planet, each warrior needs 9 minutes to repel 5 flying dragons, and 3 minutes to repel 1 ground tiger. Then, the warriors need at least $\qquad$ minutes to repel all the enemies.
$72$