What is the answers for x+2y=-8, 3y-6x=3 and y=2x+6

What is the order of magnitude for the number of liters in a large bottle of soda served at a party

The general form of the quetion of a circle is ax^2+by^2+cx+dy+e=0 where a=b=0 if the circle has a radius of three units and the center lies on the y axis which set of values of a, b, c, d, and e might correspond to the circle

What is the number 321,000,000 in scientific notation? also what is the number? ?