pipe a can fill a tank in 6 hours . due to a leak at the bottom , it takes 9 hours for the pipe a to fill the tank . in what time can the leak alone empty the full tank ?
"let the leak can empty the full tank in x hours 1 / 6 - 1 / x = 1 / 9 = > 1 / x = 1 / 6 - 1 / 9 = ( 3 - 2 ) / 18 = 1 / 18 = > x = 18 . answer : c"
divide(multiply(9, 6), subtract(9, 6))