Janelle weighed an unknown substance. It has a mass of 20.609 grams. She exposed the substance to a flame and carefully weighed the substance again. The substance then had a mass of 17.39 grams. Write an equation to determine the amount of mass, x, the substance lost.

On traditional maps, earth is represented in a flat plane, or by euclidean geometry. however, a globe is a more accurate model that comes from elliptical geometry. how does a globe represent the fact that there are no parallel lines in elliptical geometry? the equator is not parallel to any other latitudinal lines. the north and south poles are never connected by a geodesic. the geodesics connecting the north and south poles never intersect. the geodesics connecting the north and south poles intersect at both of the poles.