Let $A_1,A_2,A_3$ be the three series in AP, with same common difference ‘d’ and their first terms  $A,A+1,A+2$are  if a, b, c are 7th, 9th, 17th terms $A_1,A_2,A_3$ of  such that

$\left|\begin{array}{ccc}a& 7& 1\\ 2b& 17& 1\\ c& 17& 1\end{array}\right|+70=0$

If $a=29$ then sum of first 20 terms of an AP where first term c –a  = b with common difference $\frac{d}{12}$  is