if a man lost 4 % by selling oranges at the rate of 16 a rupee at how many a rupee must he sell them to gain 28 % ?
"96 % - - - - 16 128 % - - - - ? 96 / 128 * 16 = 12 answer : a"
divide(multiply(subtract(const_100, 4), 16), add(const_100, 28))