d 9th term of an Ap is 52 while d 12th term is 70. find sum of it's 20th term?

Answer 1

Just answered you previous post of the same question.

BTW, "find the sum of it's 20th term" is confusing.

I found the 20th term.
If you want the sum of the first 20 terms, use the values of a and d I found for you and use the formula.