Cost= Fixed cost + Variable cost

Fixed cost = 20,000 and Variable cost=8*x where x is the number of units you produce

The revenue function is the amount each unit sells for times the amount of units sold, so let y be the number of units sold, we get 10y

The profit function is revenue-cost, (note that I used y in the revenue equation instead of x, because in theory you could produce items and not sell them, but you should probably assume everything that gets produced is then sold, so put x in place on y). Just subtract the functions from the first part

Then just plug those values into the profit function