Answer
The image is formed 60 cm from the front of the mirror.
The image is 9 cm tall.
Work Step by Step
Height of the image h=3.0 cm
Object distance u= -20 cm
f= R/2 = -15 cm
We want to know the image distance v and height of the image h'.
According to the mirror equation,
$v=\frac{fu}{u-f}=\frac{-15\times-20}{-20-(-15)}cm= -60 cm$
So the image is formed 60 cm from the front of the mirror.
We know that magnification $m= \frac{h'}{h}=-\frac{v}{u}$
$⇒\frac{h'}{3.0 cm}=-\frac{-60cm}{-20cm}$
or $h'= -3\times3.0 cm= -9 cm$
The image is 9 cm tall. The negative sign shows that it is inverted.
