If the income is 24000 how can the expenditure be 1,45,000 (unless IMF is very lenient on this particular family) . If 24000 is the income then the percentages apply as they are. And the only thing the examiner is checking here, in my opinion, is the application of .16 x 3/8 x (whatever is the value regardless). So shouldn't worry much on this part and simply solve it on the face value of 24,000 income, which is expressly mentioned.