Código PHP:
   <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<TITLE>Calculo de porcentaje </TITLE>
<META content="text/html; charset=windows-1251" http-equiv=Content-Type>
<meta name="DESCRIPTION"content="Rockzillla">
<meta name="KEYWORD"content="venezuela."> 
</HEAD>
<BODY style="FONT-FAMILY: Arial" bottomMargin=0 vLink=#000000 aLink=#000000 
link=#000000 bgColor=#ffffff leftMargin=0 topMargin=0 rightMargin=0 ? size="2" 
face="arial" font>
 
<TABLE width=459 height="92" border=0 align=center cellPadding=0 cellSpacing=0>
  <TBODY> 
  <TR bordercolor="#0099FF"> 
    <TD width=459 align=left vAlign=top bordercolor="#FFFFFF"><TABLE cellSpacing=0 cellPadding=0 width=434 align=center border=0>
        <TBODY>
        <TR>
          <TD valign="top"> 
            <P align=center>
              <SCRIPT language=JavaScript>
 
 
function perc1() {
 a = document.form1.a.value/100;
 b = a*40;
 document.form1.total1.value = 40
 }
function perc2() {
 a = document.form1.c.value;
 b = 40;
 c = a/40;
 d = c*100;
document.form1.total2.value = d
 
if (d <=45){ document.bgColor='red'}
else {
if (d <=75){ document.bgColor='yellow'}
else {
if (d <= 100){ document.bgColor='green'}
 
   }
 
}
 }
 
{
 }
 
//-->
</SCRIPT>
            <P align=center> 
            <FORM name=form1>
              <TABLE width="510" height="100" border=1 cellPadding=1 cellSpacing=1>
                <TBODY><TR> 
                  <TD width="213" height="46"><font size="1"> 
                     <INPUT size=10 name=c>
                    porcentaje de 40 </font></TD>
                  <TD width="69"><font size="1">= 
                    <INPUT size=10 name=total2>
                    %</font></TD>
                  <TD width="57"><font size="1"> 
                    <INPUT onclick=perc2() type=button value=Calculo>
                    </font></TD>
                  <TD width="95"><p><font size="-1"><table width="99" border="1">
                    <tr>
                      <td width="89" height="59" name=tabla perc2()><div name=tabla onclick=perc2() align="center"  id="perc2()"></div></td>
                    </tr>
                  </table></font></p>
                  <TD align=middle 
colSpan=4> <CENTER><table><td>
                    <div align="center"> <font size="1"> 
                      <INPUT type=reset value=Reset>
                      </font></div>                  
               
<P align=center> <font face="Arial, Helvetica, sans-serif" size="2"> 
 
 
</font><BR>
<BR> 
   
 
