Marcy concludes that the following system of equations has one solution.
y = 3x + 6
y = -2x + 10
which characteristic of the equations did she use to reach this conclusion?

a.
they have different slopes.

b.
they have the same two variables.

c.
they have y on the same side of the equation.

d.
they have the same slope, but different y-intercepts.