Error Analysis

1) 

It is wrong because they did not notice that the gragh was going up by 5 instead of 1.

Answer: y=2x+9

2) 

It is wrong because they should have tried to check it on both of the equations.

Answer: (1.1,-1.5)

3) 

22 is wrong because it should have a dotted line. Number 23 is wrong because it should be shaded above the line.

4)

20 is wrong because it should have a dotted line. Number 21 is wrong because it should be shaded below the line.