Help please! I need guidance.

Consider the following for Canadian Corp (CC). CC operates in Canada and operates a retail store selling cell phones. When 1,000 phones are sold in a year the total cost per phone is $76 and when sales increases by 20% the total cost will decrease to $73. 3.7 Using the High/Low method, estimate the variable and fixed cost elements of the annual costs. 3.8 Please include the equation for the total costs. 3.9 If there were 1,150 phones sold, what would be the total cost? What is the cost per unit (rounded to a penny)