Differences between selenium tellurium and polonium

Explanation:

Selenium and tellurium are rare elements, respectively, in order of crustal abundance. However, polonium, on account of its radioactive decay, is less abundant. The main source of selenium and tellurium is the anode slime deposited during the electrolytic refining of copper.

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.