<image>(Autumn 2014 • West City District Mid-term School Exam) As shown in the figure below, in 1000 "〇" fill in a sequence of numbers \(a_{1}, a_{2}, a_{3}, \dots, a_{1000}\) such that the sum of any four adjacent "〇" is equal to -10. Given that \(a_{999} = -2x\), \(a_{25} = x - 1\), find the value of \(x\) ____; and \(a_{501} = ____\).