Hi, could someone please give me explanation and guide me steps to do these questions? Thank you very much!

7) Using the high-low method to split mixed costs, the variable rate is found to be $3 per hour and the high point is 200 hours at a total cost of $1,800. What is the fixed cost at 350 hours?

a) $600

b) $750

c) $1,050

d) $1,200

8) Using the information from Question 7. What is the total variable cost at 350 hours?

a) $600

b) $750

c) $1,050

d) $1,200

9) Using the information from Question 7. What is the estimated total cost at 350 hours?

a) $2,850

b) $3,000

c) $1,800

d) $2,250