An animal shelter spends $3.00 per day to care for each cat and $5.00 per day to care for each dog. Penelope noticed that the shelter spent $69.00 caring for cats and dogs on Tuesday. Penelope found a record showing that there were a total of 17 cats and dogs on Tuesday. How many cats were at the shelter on Tuesday

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.