Problem: find the greatest number which leaves the same remainder when it divides 21 , 57 and 105 .
Rationale: "105 - 57 = 48 57 - 21 = 36 105 - 21 = 84 the h . c . f of 36 , 48 and 84 is 12 . answer : c"
annotated_formula: divide(subtract(57, 21), const_2)