Code:
Y C I
100 110 50
200 190 50
300 270 50
400 350 50
500 430 50
by inspection, C = 30 + 0.8Y
also note equilibrium occurs when Y = C + I
so Y = 30 + 0.8Y + I,
0.2Y = 30 + I,
Y = 150 + 5*I
as I = 50, Y = 400 is the initial national income from equilibrium
if I = 50 + 30, then Y = 150 + 400
= 550