What percent of 80 is 42?

Which equation represents the partial sum of the geometric series?

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 area of the triangle 10 13 12