An object 20 cm high is placed at a distance of 100 cm from the mirror. What will be the size of the image??? How do you get this answer

Dear Student ,
Your question is not complete .It can only be answered if the mirror is assumed to be plane mirror .
Hence if the mirror is plane mirror then ,image height or image size and object size will be same or equal .
So hence the size of the image will be 20 cm .
Regards