Bro, you calculate I+X+G-S-M-T. In option B it turns out to be 0. Since, injection is equal to leakage, the national income should be 800 as given in the option.
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Economics (9708)/9708_w08_qp_3.pdf
question 16 anybody? i dont get how the answer is B?
how is consumption assumed to be 380 there?