A man 1.5meter tall stands in front of a concave mirror whose radius is 30cm. Find the position of the man that will lead to his image on the screen 20 cm. from the mirror. How big is the man's image?

Answer 1

The focal length of the mirror is R/2 = 15 cm.

You must by now be familiar with the equation
1/do + 1/di = 1/f

which in your case becomes

1/do + 1/20 = 1/15
Solve for do (the object distance). The magnification will be di/do.
Multiply that by 1.5 meters for the image size