Simplify: (4a + 2b)(a - b)

a) 4a^2 - 6ab - 2b^2
b) 4a^2 - 2ab - 2b^2
c) 4a^2 - 8ab - 2b^2
d) 4a^2 + 2ab - 2b^2

Were is the problem

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.