/home/dvjjulio/test.istyle.mx/app/ISR.php
<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use DB;

class ISR extends Model
{
    //
    protected $table = 'isr';
    public $incrementing = false;
    public $timestamps = false;

    public function get_isr($val){
      $sql = "SELECT *
              FROM isr
              WHERE limite_inferior <= $val AND
                    limite_superior > $val";

      $query = DB::select(DB::raw($sql));

      if(count($query) != null){
        return $query;
      }

    }
}