gistfile1.js

<SCRIPT language="JavaScript">
function fc(form) {
var Age   = eval(form.age.value);
var Freq = (210 * ((Age - 18)/71)*((Age - 18)/71)) - (311*(Age - 18)/71) + 133
form.freq.value = parseInt(Freq)
}
</script>

<FORM METHOD = "post">
Age: <INPUT name= "age" value="18" size="2" type="text">
Freq: <INPUT name= "freq" value="  " size="3" type="text">
<INPUT value="Solve" onclick="fc(this.form)" type="button">
</form>

<SCRIPT language="JavaScript">
function fl(form) {
var Age   = eval(form.age.value);
var Freq = (210 * ((Age - 18)/71)*((Age - 18)/71)) - (290*(Age - 18)/71) + 124
form.freq.value = parseInt(Freq)
}
</script>

<FORM METHOD = "post">
Age: <INPUT name= "age" value="18" size="2" type="text">
Freq: <INPUT name= "freq" value="  " size="3" type="text">
<INPUT value="Solve" onclick="fl(this.form)" type="button">
</form>

<SCRIPT language="JavaScript">
function m(form) {
var Age   = eval(form.age.value);
var Freq = (210 * ((Age - 18)/71)*((Age - 18)/71)) - (276*(Age - 18)/71) + 128
form.freq.value = parseInt(Freq)
}
</script>

<FORM METHOD = "post">
Age: <INPUT name= "age" value="18" size="2" type="text">
Freq: <INPUT name= "freq" value="  " size="3" type="text">
<INPUT value="Solve" onclick="m(this.form)" type="button">
</form>