Answer:
3x - y = - 9
Explanation:
the equation of a line in standard form is
Ax + By = C ( A is a positive integer and B, C are integers )
rearrange y = 3x + 9 into this form
subtract y from both sides
0 = 3x - y + 9 ( subtract 9 from both sides )
3x - y = - 9 ← in standard form