Carrie spent  1
4
 of her allowance on a shirt, 
1
3
 of her allowance on a skirt, and $8 on a belt. If she spent $22 in all, how much was Carrie’s allowance?

Equation: 
1
4
a +
1
3
a + 8 = 22

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.