Discover Questions

Is there a musical term for two independent, non-complementary, parts being played simultaneously? What about for three parts? Could someone help me with these math problems? I can't figure them out. Solve the linear equation;
x+2y=15
y=-2x+0 9x-12y=-3
-12x+16y=4? How many edges in a circle? Diameter of a wheel 80cm. If the wheel rotates through an angle of 200degrees, how many cm does it move? Show steps please!? Does NASA still use miles instead of kilometers?