1) Computation of Opportunity Cost:

Opportunity cost of spending 10 hours planting seeds = 10 hours of music lesson lost = 10 * $20 = $200 ( Implicit cost )

2) His accountant would only measure the explicit cost of seeds = $100

3) Computation of Accounting Profit:

Accounting Profit = Total Revenue - Explicit Costs = $200 - $100 = $100

4) Computation of Economic Profit:

Economic profit = Total revenue - Explicit costs - Implicit costs = 200 - 100 - 200 = 200 - 300 = - $100 ( loss )