A concave mirror produces a real image of 10mm tall of an object 2.5 mm tall placed at a 5 cm from the mirror calculate the focal length of the mirror and the position of the image

Given that , $h_i=10 mm , and , h_o=2.5 mm$
$magnification , m= -\frac{v}{u}=\frac{h_i}{h_o}$
where v is the image distance , u is object distance , 

u = -5cm ,

v= 4(u) so , v = (-5) (4) i.e. -20cm

 here minus sign indicates that the mirror is concave mirror

Regards