#g(x)# is the inverse of #f(x)# if #f(g(x))=x# for all #x#
If #f(color(blue)x)=6color(blue)x#
then #color(white)("XXX")f(color(blue)(g(color(red)x)))=6 * color(blue)(g(color(red)x))#
and if #color(white)("XXX")6 * color(blue)g(color(red)x)=x#
then #color(white)("XXX")color(blue)(g(color(red)x))=x/6#