#"given:"#
#f:"focus :r:radius ;g:length of image ; c:length of object"#
#u="distance between object and mirror"#
#u'="distance between image and mirror"#
#r=60" cm ; f="60/2="30 cm"#
#g/c=(u')/u" ; "6/10=(u')/u" ; "u'=(6u)/10#
#-1/f=1/u-1/(u')" equation for convex mirrors"#
#-1/30=1/u-1/((6u)/10)#
#-1/30=1/u-10/(6u)#
#-1/30=(6-10)/(6u)#
#-1/30=-4/(6u)#
#120=6u#
#u=20" cm"#