.
5x + 6y = -15
15x + 18y = -45
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The coefficients of the second equation are those of the first equation multiplied by 3. The right sides are in the same proportion.
Hence, the system is dependent and consistent.
It actually represents the same equation and the same straight line.
Infinitely many solutions.
You can take any value of x and calculate the corresponding value of y.
They will fit both equations.
See the lesson Geometric interpretation of the linear system of two equations in two unknowns in this site.