Step 1) Because the second equation is already solved for #y#, substitute #5x + 27# for #y# in the first equation and solve for #x#:
#9x - 9y = -27# becomes:
#9x - 9(5x + 27) = -27#
#9x - 45x - 243 = -27#
#-36x - 243 = -27#
#-36x - 243 + color(red)(243) = -27 + color(red)(243)#
#-36x - 0 = 216#
#-36x = 216#
#(-36x)/color(red)(-36) = 216/color(red)(-36)#
#(color(red)(cancel(color(black)(-36)))x)/cancel(color(red)(-36)) = -6#
#x = -6#
Step 2) Substitute #-6# for #x# in the second equation and calculate #y#:
#5x + 27 = y# becomes:
#(5 xx -6) + 27 = y#
#-30 + 27 = y#
#-3 = y#
#y = -3#
The solution is #x = -6# and #y = -3# or #(-6, -3)#
