#[macro_export]
macro_rules! read_line {
    ($($xs: tt)*) => {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        let mut iter = buf.split_whitespace();
        expand!(iter, $($xs)*);
    };
}

#[macro_export]
macro_rules! expand {
    ($iter: expr,) => {};
    ($iter: expr, mut $var: ident : $type: tt, $($xs: tt)*) => {
        let mut $var = value!($iter, $type);
        expand!($iter, $($xs)*);
    };
    ($iter: expr, $var: ident : $type: tt, $($xs: tt)*) => {
        let $var = value!($iter, $type);
        expand!($iter, $($xs)*);
    };
}

#[macro_export]
macro_rules! value {
    ($iter:expr, ($($type: tt),*)) => {
        ($(value!($iter, $type)),*)
    };
    ($iter: expr, [$type: tt; $len: expr]) => {
        (0..$len).map(|_| value!($iter, $type)).collect::<Vec<_>>()
    };
    ($iter: expr, Chars) => {
        value!($iter, String).unwrap().chars().collect::<Vec<_>>()
    };
    ($iter: expr, $type: ty) => {
        if let Some(v) = $iter.next() {
            v.parse::<$type>().ok()
        } else {
            None
        }
    };
}

fn main() {
    read_line!(t: usize,);

    for _ in 0..t.unwrap() {
        read_line!(l: isize, r: isize, a: isize, b: isize,);

        let l = l.unwrap();
        let r = r.unwrap();
        let a = a.unwrap();
        let b = b.unwrap();

        let f = |x| a * x + b;

        println!("{}", if a > 0 { f(r) } else { f(l) });
    }
}