後半部分に <table> を出力するための <output> を追加.
<div align='center'>
<table border='0'>
<tr>
<td>
<span align="center">A : B = C : x</span><br/>
<hr/>
A <input type='number' id='in__a' value='25' style='width:80px;' step='any' /> <br />
B <input type='number' id='in__b' value='1' style='width:80px;' step='any' /> <br />
C <input type='number' id='in__c' value='500' style='width:80px;' step='any' /> <br />
<hr/>
<input type='submit' id='cal_x' value='  x  '/> <span id='out_x'> </span>
</td>
</tr>
</table>
<hr/>
<output id='out_l'>
</output>
<br/>
</div>
<table>~</table> を作成して <output> の所に設定.
function make_lst () {
let ol = document.getElementById("out_l") ;
let ox = document.querySelector("#out_x") ;
let s_tb = "<table border='1'>" ;
let s_dt = "<tr> <td>" ;
let dt_e = "</td> </tr>" ;
let tb_e = "</table>" ;
let t_dt = "" ;
t_dt = t_dt + s_tb ;
let index = 0 ;
let data = 0 ;
for (index=0 ; index<10 ; index++) {
t_dt = t_dt + s_dt ;
data = index * ox.textContent ;
data = data.toPrecision(5) ;
t_dt = t_dt + data ;
t_dt = t_dt + dt_e ;
}
t_dt = t_dt + tb_e ;
ol.innerHTML = t_dt ;
}
function x_click () {
calc_x () ;
make_lst () ;
}