So the original amount of money in the bank account is given by a negative number: -$21. If you deposit $6 per day during four days then the total amount of money deposited by the fourth day is:
[tex]4\cdot\text{\$}6=\text{\$}24[/tex]The total amount of money in the account is given by adding the deposited money to the original amount:
[tex]-\text{\$}21+\text{\$}24=\text{\$}3[/tex]Then the answer is $3.
