Why is an element considered a pure substance? im i right

An element is considered a pure substance because it is made up of only one type of atom and cannot be broken down into a simpler form.

The path of a satellite orbiting the earth causes it to pass directly over two tracking stations a and b, which are 51 miles apart. when the satellite is on one side of the two stations, the angles of elevation at a and b are measured to be 87 degrees and 84 degrees, respectively. (a) how far is the satellite from station a? (b) how high is the satellite above the ground?