Answer 1

Cause CTO should have implemented method workHard()
And be static

Answer 2

And it is no sense
Parent implement Businessman
CTO extends Parent implement Businessman
You should or extends parent or implement businessman, cause you parent class already has it

Answer 3

Gangadhar All your interface and classes are inside the Solution class. Is it intentional or you did it by mistake? Also workHard() has no implementation so there will be no output whatsoever.