#-67 = -4n + 3(1 + 6n)#
#-67 = -4n + 3 + 18n#
#-67 color(red)(-3) = -4n color(red)(cancel(color(black)(+ 3) -3)) + 18n#
#-70 = -4n + 18n#
#-70 = 14n#
#-70/14 = (color(red)(cancel(color(black)(14)))n)/color(red)(cancel(14))#
#n = -70/14#
#color(blue)(n = -5#
Now we can substitute #n# for #-5# to prove our answer.
#-67 = -4 xx -5 + 3(1 + 6 xx -5)#
#-67 = -4 xx -5 + 3(1 + -30)#
#-67 = -4 xx -5 + 3 xx -29#
#-67 = 20 + 3 xx -29#
#-67 = 20 + -87#
#-67 = -67#