Hi Cordelia To account for the loss of Investment A you could create a journal entry that credits the asset account and debits an expense account, you can create a specific expense account for this loss, lets say name it 'Investment A write off'. This will remove the amount from the balance sheet and show as an expense/loss on your P&L.
To account for sale/closure of Investment B including the profit you could create a journal entry that credits the asset account, in your example, by 200, debit the bank account by 250 and then credit 50 to an income account, again you can create a specific income account and name it, lets say 'profit of investment B'. This will remove the 200 from the balance sheet, show 250 in your bank account and 50 on your P&L.
Please note that we're not accountants and any advise we give should be qualifies by an accountant.
