Mr. Kelly runs a basketball camp for middle school students. Mr. Kelly buys each student who attends the camp a t-shirt for participating. The t-shirts cost $5 each. There is a proportional relationship between the number of students who attend Mr. Kelly’s basketball camp, x, and the total cost of the t-shirts, y.

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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.