{"solution": "Option 1 -> This represents the initial equilibrium output when c = 0.8, not the change.
Option 2 -> This is the new equilibrium output when c = 0.5, not the change in output.
Option 3 -> This correctly represents the change in equilibrium output (250 - 100 = 150).
Option 4 -> This value doesn't match any relevant calculation in this problem.
Hence, Option 3: 150 -> Using the Keynesian multiplier model, equilibrium output Y = A/(1-c). When c = 0.8: Y₁ = 50/(1-0.8) = 50/0.2 = 250. When c = 0.5: Y₂ = 50/(1-0.5) = 50/0.5 = 100. The change in equilibrium output = 250 - 100 = 150. As the marginal propensity to consume decreases, the multiplier effect weakens, leading to a lower equilibrium output -> correct"}