Option 1 -> This is the equilibrium output when I = 10 (initial investment), not when I = 20.
Option 2 -> At equilibrium Y = C + I, so Y = 40 + 0.8Y + 20. Solving: 0.2Y = 60, thus Y = 300.
Option 3 -> Incorrect calculation of equilibrium output.
Option 4 -> Incorrect calculation of equilibrium output.
Hence, Option 2: 300 -> At equilibrium, Y = C + I. Substituting the values: Y = 40 + 0.8Y + 20, which gives Y = 60 + 0.8Y. Rearranging: Y - 0.8Y = 60, therefore 0.2Y = 60, and Y = 300. The multiplier effect (k = 1/(1-MPC) = 1/0.2 = 5) amplifies the increase in investment (ΔI = 10) to create a total change in output of 50 units (from 250 to 300). -> correct