What are the three main gases that make up the atmosphere?

Nitrogen — 78 percent.

Oxygen — 21 percent.

Argon — 0.93 percent.

Carbon dioxide — 0.04 percent.

Trace amounts of neon, helium, methane, krypton and hydrogen, as well as water vapor.

a: 45.9 meters

b: 4.29 seconds

step-by-step explanation:

a: h(t)=1/2(-9.8)(3)^2+0(3)+90

h(t)=-4.9(3)^2+90

h(t)=-44.1+90

h(t)=45.9 meters

b: 0=1/2(-9.8)(t^2)+0t+90

0=-4.9t^2+90

-90=-4.9t^2

18.37=t^2

t=4.29 seconds

in the second question, the numbers aren't exact, but they're a close approximation.