Several intervals can be combined into one region using the "set union" operation, ∪∪, which is represented as "U" in WeBWorK. For example, [-2,0] U (8,inf) represents the points from −2−2 to 00 together with everything bigger than 8. Write the set of points from −6−6 to 22 but excluding −3−3 and 22 as a union of intervals:

Planet earth has a mass of 5.9726x10²⁴ kg.then: 5.9726x10²⁴ kg=100% of the total earth mass.if the water´s mass=5x10-4 % of the total mass, we can solve this problem by the rule of three.5.9726x10²⁴ %*10⁻⁴ %x=(5.9726x10²³ kg)(5*10⁻⁴  %) / 100 %=2.9863x10¹⁹ kganswer:   the mass of the planet´s water would be   2.9863 x 10¹⁹ kg.