Your economic profit for 2015 is $70,000.
Economic profits are calculated by using the formula:
Economic Profit = Sales - (Explicit Costs + Implicit Costs)
Explicit Costs are costs that are incurred in the normal course of a business like cost of materials, wages, rent etc. In this question, cost of materials and assistant's salary are the explicit costs.
Implicit Costs or opportunity costs refer to the returns an individual misses out on account of making a choice. In the given context, you chose to start a business; however, if you had chosen to remain employed elsewhere, you would have earned $60,000. So, this $60,000 is an implicit cost or an opportunity cost.
So, Economic Profit is calculated as:
Economic Profit = $200,000 - ($50,000+ $20,000 + $60,000)
Economic Profit = $70,000.