Problem: find the average of all numbers between 1 and 13 which are divisible by 2
Rationale: "explanation : average = ( 2 + 4 + 6 + 8 + 10 + 12 ) / 2 = 42 / 2 = 21 option b"
annotated_formula: divide(add(add(add(multiply(2, const_3), add(2, multiply(2, const_2))), multiply(2, const_4)), multiply(add(const_4, const_1), 2)), 2)