Let the sum of an infinite G.P., whose first term is a and the common ratio is \(r\), be 5 . Let the sum of its first five terms be \(98/25\). Then the sum of the first 21 terms of an A.P., whose first term is \(10ar,n^{\text{th}\text{~}}\) term is \(a_{n}\) and the common difference is \(10ar^{2}\), is equal to\