Match the systems of equations to their solutions. 2x + y = 12
x = 9 - 2y
x + 2y = 9
2x + 4y = 20
x + 3y = 16
2x - y = 11
y = 11 - 2x
4x – 3y = -13
y = 10 + x
-3x + 3y = 30
2x + y = 11
x - 2y=-7

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.