Given
#color(white)("XXX")(-6m-3)/4=(2m+5)/(-2)#
#rArrcolor(white)("XXX")(-6m-3)/color(magenta)4=(2m+5)/(-2)color(orange)( xx (-2)/(-2)) = (-4m-10)/color(magenta)4#
#rArrcolor(white)("XXX")-6m-3=-4m-10#
#rArrcolor(white)("XXX")6m+3=4m+10#
#rArrcolor(white)("XXX")2m=7#
#rArrcolor(white)("XXX")m=3 1/2#