Problem: find the number which is nearest to 3105 and is exactly divisible by 21 .
Rationale: "sol . on dividing 3105 by 21 , we get 18 as remainder . number to be added to 3105 = ( 21 - 18 ) - 3 . hence , required number = 3105 + 3 = 3108 . option b"
annotated_formula: add(3105, subtract(21, reminder(3105, 21)))