Problem: the average of 5 quantities is 9 . the average of 3 of them is 4 . what is the average of remaining 2 numbers ?
Rationale: "answer : a ( 5 x 9 - 3 x 4 ) / 2 = 16.5"
annotated_formula: divide(subtract(multiply(5, 9), multiply(3, 4)), 2)