Answer:
I think the answer is B. I could be wrong tho, love.
Answer:
The demabd function is:

Step-by-step explanation:
The demand follow the linear equation 
1. When p=$2.00 and q=9000, the equation is:

2. Whe p=$4.00 and q=0, the equation is:

3. Solve equation (1) for b:

4. Replace the value of b in equation (2)

The value of m is 4500
5. Calculate b, replacing m:

The value of b is 18000
Answer: d. He multiplied when he was supposed to divide
Step-by-step explanation:
He just multiplied across when he was supposed to divide (or cross multiply) to find the unit rate :)