8a) The first and third terms of an arithmetic series are 3 and 27 respectively. i) find the common difference ii) find the sum of the first 11 terms of the series b) find the sum of the inteers between 50 and 150 which are divisible by 8. I have already done part a) and found the common difference to be 12 and the sum of the first 11 terms to be 693. But i have no idea how to start part b, any suggestions please??