A perfectly competitive industry is initially in a short-run equilibrium in which all firms are earning zero economic profits but are operating below their minimum efficient scale. Explain the long-run adjustments that will create equilibrium

A perfectly competitive industry is initially in a short-run equilibrium in which all firms are earning zero economic profits but are operating below their minimum efficient scale. Explain the long-run adjustments that will create equilibrium with firms operating at their minimum efficient scale. Why is a perfect competitive firm associated with efficiency for both consumers and businesses?