Once price is below average cost the farm loses money whatever it does, so the question is which choice loses least. Shutting down still leaves the fixed cost of $62 to pay. Staying open is better whenever price covers average variable cost, because every pack then pays its own variable cost and contributes something toward the fixed cost.
In (a), at $2.00, the farm produces 65 packs and loses about $47, less than the $62 it would lose by closing, so it stays open. In (b), at $1.50, price is below average variable cost at the 60 packs where P = MC: revenue would be $90 against total cost of $165, a loss of $75, worse than the $62 from shutting down. The shutdown point is the minimum of average variable cost, about $1.72. The sliders set the price in each panel.