use std::cmp::*;
#[allow(unused_imports)]
use std::collections::*;
use std::io::Read;

fn get_word() -> String {
    let stdin = std::io::stdin();
    let mut stdin = stdin.lock();
    let mut u8b: [u8; 1] = [0];
    loop {
        let mut buf: Vec<u8> = Vec::with_capacity(16);
        loop {
            let res = stdin.read(&mut u8b);
            if res.unwrap_or(0) == 0 || u8b[0] <= b' ' {
                break;
            } else {
                buf.push(u8b[0]);
            }
        }
        if buf.len() >= 1 {
            let ret = String::from_utf8(buf).unwrap();
            return ret;
        }
    }
}

#[allow(dead_code)]
fn get<T: std::str::FromStr>() -> T {
    get_word().parse().ok().unwrap()
}

fn main() {
    let t: usize = get();
    for _ in 0..t {
        let l: i32 = get();
        let r: i32 = get();
        let a: i32 = get();
        let b: i32 = get();
        let ans = max(a * l + b, a * r + b);
        println!("{}", ans);
    }
}