Demand Estimation and Elasticity 7 Questions of long algebra formulas

This is very advanced math (Algebra) that requires each step of equation to be written out and explained (a sample is provided below). The 7 questions to be answered are in attached document. 

The teacher already has answers posted on Chegg and Course Hero please do original work. 

  
Solve for equilibrium and quantity.

Given: Monthly quantity demand function for a product is Qd = 10,000-80P and monthly quantity supply function for a product is Qs=20P.

Here is an example of how to present you work on this problem which would allow me to follow your steps:

1)    Qd=Qs   which is also equal to:

2)    10,000 – 80P = 20P

Next add 80P to both sides and divide by 100 to get:

10,000 =100p

Divide by 100 to get P by itself:
100 = P

This is equilibrium price. 

Next, you need equilibrium quantity.

Plug the equilibrium price (100) into either  demand or supply function. 
If we plug it into the demand function you get:

Qd= 10,000 – 80*100 = 2,000

(80*100 is 8,000 and 10,000 minus 8,000 is 2,000)

If you plug it into the supply function you get:

Qs = 20*100 = 2,000

Here, the quantity supplied is equal to the quantity demanded.