First things first, please run composer install
after cloning.
You do not need to change any class code. Just write your plain code.
Calculate Triangle:
echo 'Calculate Triangle: ' . (new Engineer())->calculateArea (10, 10, new Triangle());
Calculate Rectangle:
echo 'Calculate Rectangle: ' . (new Engineer())->calculateArea (10, 10, new Rectangle());
Calculate Circle:
echo 'Calculate Circle: ' . (new Engineer())->calculateArea (10, 0, new Circle());