I wrote a program for calculating the graphic area according to the book, but did not perform the calculation. I would like to know where the error occurred.

I wrote a program for calculating the graphic area according to the book, but did not perform the calculation. what is the last example of the error in chapter 8th of php. You can create a form, but an error occurs after you click calculate. Could you kindly advise the interface: class _ Shape. php & lt ;? Php & nbsp;
The last example in chapter 8th of php. You can create a form, but an error occurs after you click calculate. Thank you!
Interface: class _ Shape. php
Interface Shape {
Function area ();
Function perimeter ();
}
?>
Rectangle: class _ Rect. php
Class Rect implements Shape {
Private $ width;
Private $ length;

Function _ construct ($ size = ""){
$ This-> width = $ size ["width"];
$ This-> length = $ size ["length"];
}
Function area (){
Return $ this-> length * $ this-> width;
}
Function perimeter (){
Return 2 * ($ this-> width + $ this-> length );
}
}
?>
Triangle: class _ Triangle. php
Class Triangle implements Shape {
Private $ length1;
Private $ leng2;
Private $ length3;

Function _ construct ($ size = ""){
$ This-> length1 = $ size ["length1"];
$ This-> lengh2 = $ size ["leng2"];
$ This-> length3 = $ size ["length3"];
}
Function area (){
$ S = ($ this-> length1 + $ this-> length1 + $ this-> length3)/2;
Return sqrt ($ s * ($ s-$ this-> length1) * ($ s-$ this-> length1) * ($ s-$ this-> length3 ));
}
Function perimeter (){
Return $ this-> length1 + $ this-> length1 + $ this-> length3;
}
}
?>
Circle: class _ Circle. php
Class Circle implements Shape {
Private $ radius;

Function _ construce ($ size = ""){
$ This-> radius = $ size ["radius"];
}
Function area (){
Return pi () * $ this-> radius;
}
Function perimeter (){
Return 2 * pi () * $ this-> radius;
}
}
?>
Table: class _ Form. php
Class Form {
Private $ formName;
Private $ request;
Private $ action;
Private $ method;
Private $ target;

Function _ construct ($ formName, $ request, $ action = "index. php", $ method = "get", $ target = "_ self "){
$ This-> formName = $ formName;
$ This-> request = $ request;
$ This-> action = $ action;
$ This-> method = $ method;
$ This-> target = $ target;
}
Function _ toString (){
$ Str =" ";
$ Str. ="". $ This-> formName ."";
$ Str. =" Action. "method =". $ this-> method. "target = $ this-> target ";

Switch ($ this-> request ["action"]) {
Case 1:
$ Str. ="Rectangular length:";
$ Str. =" Request ["length"]. ">";
$ Str. ="Rectangle width:";
$ Str. =" Request ["width"]. ">";
Break;
Case 2:
$ Str. ="Triangle side length 1:";
$ Str. =" Request ["length1"]. ">";
$ Str. ="Triangle side length 2:";
$ Str. =" Request ["leng2"].">";
$ Str. ="Triangle side length 3:";