The submission needs work, and I am unsure how to write the feedback. Certainly, your mastery of the math is very good. As stated elsewhere however, this is a course in economics, and the competencies that must be mastered in this assessment include the the theories, models, and practices of macro and micro economic theory and practice as they apply to corporate operations to create value for the firm.
What this means is that simple explanations of the formulas and statements that this is the way it is are not enough.
Consider how you would approach the problem if you were tasked to explain the information in the assessment to your CEO or Board of Directors.
You don't walk in and launch into the math or one-two sentence overviews of what is important to them for making real-world decisions.
You introduce the topic, explain what is going to take place/be discussed, and tell them why it is important for their decision-making processes. Then you tell them; taking the time to explain what is going on in terms that apply to their decision-making and operating activities.
You don't tell them all about the math.
That is what you need to do in these assessments. Tell about the problems from the point of view applicable to the decision-makers, not a mathematician or accountant.