Answer:
![y = -x-1](https://img.qammunity.org/2021/formulas/mathematics/middle-school/hxsjsplapmf5s8lactjum526cqipfe3pyp.png)
Explanation:
The Slope-Intercept form of the equation of the line is:
![y=mx+b](https://img.qammunity.org/2021/formulas/mathematics/middle-school/yj5waqmoy4i54laybzhhshd88hyo5w5rj5.png)
Where "m" is the slope and "b" is the y-intercept.
When you have a System of Linear equations and the lines are exactly the same line, you can identify that the System has Infinitely many solutions.
In this case, you know that the Line M is represented by the following equation:
![x + y = -1](https://img.qammunity.org/2021/formulas/mathematics/middle-school/16xviaa52owko8hslrm5pgi2dmc6r0g0wl.png)
Solving for "y" , you get:
![y = -x-1](https://img.qammunity.org/2021/formulas/mathematics/middle-school/hxsjsplapmf5s8lactjum526cqipfe3pyp.png)
You can identify that:
![m=-1\\\\y=-1](https://img.qammunity.org/2021/formulas/mathematics/middle-school/mdayt2wex1sjf3bk54p6h2np43nionco9r.png)
Therefore, to the set of equations has infinitely many solutions, the Line M and the Line P must be exactly the same.
Then, you can determine that the Line P is represented by the following equation:
![y = -x-1](https://img.qammunity.org/2021/formulas/mathematics/middle-school/hxsjsplapmf5s8lactjum526cqipfe3pyp.png)