Discover Questions

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 molecules are in 97.8g of FeCl3? If x^2+y^2 = 6, and x+y=3, then what is x^3+y^3? Does NASA still use miles instead of kilometers? How to locate/take pictures of planets?