1)Why would sending only a small group of people to settle Mars be considered a bad idea for the future of the population ? 2)Why did it take so long for the Americas to finally be successfully colonized ?

i dont know this but ask your teacher for !

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)

oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%