During the synthesis stage of the cell cycle, a cell makes (replicates its own) DNA.
Economic profits equals total revenues minus the sum of explicit costs and implicit costs. Since explicit costs are already subtracted when arriving at the accounting profit, we can find economic profit by subtracting the implicit costs from the accounting profit.
Economic profit is calculated as : Accounting profit from existing product line - profit that could have been earned had he invested in other product line = Economic profit. If the economic profit is positive, stay put. If it is negative, exit. Economic profits will start accruing in late childhood, will reach peak in adulthood, and will taper down in middle age. Economic profits will be negative after late middle age.