Vision-Box interview question

1) They provided me some code and ask me to do the code refraction. Also if i can implement any design pattern also the solid principles. 2) Oops concepts 3) Abstract vs interface 4) what is sealed classes 5) what are the access modifiers 6) what is private constructor why do we have private constructor. 7) Static class and constructor etc Manager asked me below question 1) how do you handle performance issue in your application 2) what do you understand by seeing vision box site 3) do you know anything about our company ? Tech Round 2 ) Managerial + HR 1) what is your current work and roles and responsibility 2) Most of the behavioral questions