Let S be the amount he can sell it for in Bombay. 100- 15= 85 so it costs .85S in Nasik. So his "gross profit" buying it for .85S and selling it for S is, of course, S- .15S= .85S (We should have seen that coming!). Because it cost him 150 to travel, his net profit is .85S- 150 and we are told that is 150 also. So we need to solve .85S- 150= 150 for S. To get his percent profit (as a perencent of his cost) divide 150 by .85S.