find the average of all the numbers between 6 and 30 which are divisible by 4 .
"sol . average = ( 8 + 12 + 16 + 20 + 24 + 28 / 6 ) = 108 / 6 = 18 answer b"
divide(add(add(6, const_4), subtract(30, const_4)), const_2)