The error lies in the beginning of step 2
-x was substituted in the place of x in first line of step 2
Correction of the error and solution is given below
Step 1
-x + 4y = -9
-x = -4y -9
multiply both sides by -1, we have
x = 4y + 9
Step 2
3( 4y + 9) -2y =7
12y +27 -2y = 7
10y +27 = 7
10y = 7-27
10y = -20
y = -20/10
y = -2
