Problem: find the average of all the numbers between 6 and 34 which are divisible by 5 .
Rationale: "solution average = ( 10 + 15 + 20 + 25 + 30 / 5 ) = 100 / 5 = 20 . answer b"
annotated_formula: divide(add(add(6, const_4), subtract(34, const_4)), const_2)