Ghumdai firdai rumjhaltar, bhanya jasto. Equilibrium level of GDP is 620. In an economy without govt. role and foreign trade, we do not need to beat around the bush. Pluck the value of C and I, and they you'll gey Y. Voila! -> MPC is given. -> Change is Y & Change in I is NOT in the question and hence why go there? -> C and I is given. And you do not need to worry about govt. tax and foreign trade, thus the formula including those facets are nonessential here. Based on the requirement that desired expenditure equals output (C+I = Y) with a touch of basic algebra, the equilibrium level of GDP can be calculated. For your convenience, the value of C is also plucked in, which includes the MPC (change in consumption/change in income ). I have posted it in two lines above in my last post. Now what part of the solution do you not understand? Yeso hernu paryo kaji! IndisGuise:s Disclaimer: Maile bujeko jatti bhaneko ho. Galti bhaye ma jimmebaar chuina. ;)