1) Aarush bakes 3 cakes. Each cake uses 2.7 cups of sugar. How much sugar does he use altogether?

Since each cake uses 2.7, you multiply 3 by 2.7:
3 * 2.7 = 8.1
Solution: he uses 8.1 cups of sugar

The answer of the above question is

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.