// ---------- begin scannner ----------
#[allow(dead_code)]
mod scanner {
    use std::str::FromStr;
    pub struct Scanner<'a> {
        it: std::str::SplitWhitespace<'a>,
    }
    impl<'a> Scanner<'a> {
        pub fn new(s: &'a String) -> Scanner<'a> {
            Scanner {
                it: s.split_whitespace(),
            }
        }
        pub fn next<T: FromStr>(&mut self) -> T {
            self.it.next().unwrap().parse::<T>().ok().unwrap()
        }
        pub fn next_bytes(&mut self) -> Vec<u8> {
            self.it.next().unwrap().bytes().collect()
        }
        pub fn next_chars(&mut self) -> Vec<char> {
            self.it.next().unwrap().chars().collect()
        }
        pub fn next_vec<T: FromStr>(&mut self, len: usize) -> Vec<T> {
            (0..len).map(|_| self.next()).collect()
        }
    }
}
// ---------- end scannner ----------

use std::io::Write;

fn main() {
    use std::io::Read;
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).unwrap();
    let mut sc = scanner::Scanner::new(&s);
    let out = std::io::stdout();
    let mut out = std::io::BufWriter::new(out.lock());
    run(&mut sc, &mut out);
}

fn run<W: Write>(sc: &mut scanner::Scanner, out: &mut std::io::BufWriter<W>) {
    let t: u32 = sc.next();
    for _ in 0..t {
        let n: usize = sc.next();
        let k: usize = sc.next();
        let a: Vec<usize> = sc.next_vec(n);
        if let Some(a) = solve(k, a) {
            writeln!(out, "{}", a).ok();
        } else {
            writeln!(out, "-1").ok();
        }
    }
}

fn solve(k: usize, a: Vec<usize>) -> Option<usize> {
    let s = a.iter().sum::<usize>();
    if s % k != 0 {
        return None;
    }
    let mut b = a.iter().map(|a| *a % k).collect::<Vec<_>>();
    let n = a.len();
    for _ in 0..(n + 1) {
        let s = b.iter().sum::<usize>();
        let m = *b.iter().max().unwrap();
        if s / k >= m {
            return Some(s / k);
        }
        let x = (0..n).filter(|x| b[*x] < a[*x]).min_by_key(|x| b[*x]).unwrap();
        b[x] += k;
    }
    None
}