虫食い算

calc.js

//    2x
// *  yz
// =====
//   ?3?
//  ???
// =====
//  ?4?

for (let x = 0; x < 10; x++) {
  for (let z = 0; z < 10; z++) {
    const t = (20 + x) * z;
    const t10 = t / 10 % 10 | 0;
    if (t10 === 3) {
      for (let y = 1; y < 10; y++) {
        const r = (20 + x) * ((y * 10) + z);
        const r10 = r / 10 % 10 | 0;
        if (r10 === 4 && r < 1000) {
          console.log("   2%s", x);
          console.log("*  %s%s", y, z);
          console.log("=========");
          console.log("  %s", t);
          console.log("  %s", (20 + x) * y);
          console.log("=========");
          console.log("  %s", r);
          console.log("");
          return;
        }
      }
    }
  }
}

res.txt

   27
*  35
=========
  135
  81
=========
  945