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());