Let the sum of the first $n$ terms of a non-constant A.P., $a_{1},a_{2},a_{3},\ldots\ldots.$. be $50n + \frac{n(n - 7)}{2}A$, where $A$ is a constant. If $d$ is the common difference of this A.P., then the ordered pair ( $d,a_{50}$ ) is equal to