Given that the first term of an AP is 7and it's 10th term is twice the second term.calculate the sum of it's 28th terms and the difference between the 9th and 6th term.
a = 7
a+9d = 2(a+d)
Solve for d, and then find (I think, since your English is garbled)
(a+27d) + ((a+8d)-a+5d)