Step 1) Solve the second equation for #y#:
#-x + y = -4#
#-x + color(red)(x) + y = -4 + color(red)(x)#
#0 + y = -4 + x#
#y = -4 + x#
Step 2) Substitute #(-4 + x)# for #y# in the first equation and solve for #x#:
#2x - y = 7# becomes:
#2x - (-4 + x) = 7#
#2x + 4 - x = 7#
#2x - x + 4 = 7#
#2x - 1x + 4 = 7#
#(2 - 1)x + 4 = 7#
#1x + 4 = 7#
#x + 4 = 7#
#x + 4 - color(red)(4) = 7 - color(red)(4)#
#x + 0 = 3#
#x = 3#
Step 3) Substitute #3# for #x# in the solution to the second equation at the end of Step 1 and calculate #y#:
#y = -4 + x# becomes:
#y = -4 + 3x#
#y = -1#
The Solution Is:
#x = 3# and #y = -1#
Or
#(3, -1)#