Script:

    var total = 0;
    
    for (var i = 1; i < 100; i++) {
      for (var j = 1; j < 100; j++) {
        for (var k = 1; k < 100; k++) {
          total = 15*i + j + 0.25*k;
          
          if (total == 100 && (i + j + k == 100)) {
            document.write("Dogs: " + i + " Cats: " + j + " Mice: " + k);
            break;
          }
          
          total = 0;
        }
        
        if (total) {
          break;
        }
      }
      
      if (total) {
        break;
      }
    }