First, multiply each side of the equation by #color(red)(56 - M)# to eliminate the fraction:

#-0.50 xx (color(red)(56 - M)) = (47 - M)/(56 - M) xx (color(red)(56 - M))#

#-28 + (0.50 xx- M) = (47 - M)/color(red)(cancel(color(black)((56 - M)))) xx cancel((color(red)(56 - M)))#

#-28 + (0.50M) = 47 - M#

#-28 + (0.50M) + color(blue)(28) + color(red)(M) = 47 - M + color(blue)(28) + color(red)(M)#

#-28 + color(blue)(28) + (0.50M) + color(red)(M) = 47 + color(blue)(28) - M + color(red)(M)#

#0 + 1.50M = 75 - 0#

#1.50M = 75#

#(1.50M)/color(red)(1.50) = 75/color(red)(1.50)#

#(color(red)(cancel(color(black)(1.50)))M)/cancel(color(red)(1.50)) = 50#

#M = 50#