The system of equations has infinitely many solutions.
To solve the system of equations:
-5x - 7y = -7
-15x - 21y = -21
We can use the method of substitution or elimination. We will use the elimination method.
Multiply the first equation by 3, and the second equation by -1 to eliminate the 'x' term:
-15x - 21y = -21
15x + 21y = 21
Add the two equations together to eliminate the 'x' term:
0x + 0y = 0
Simplify the equation to get:
0 = 0
The resulting equation, 0 = 0, is always true. This means that the system of equations has infinitely many solutions, or in other words, the two equations represent the same line on a graph.