Jane made an initial deposit to a savings account. Each week thereafter she deposited a fixed amount to the account. The equation above models the amount a, in dollars, that Jane has deposited after weekly deposits. According to the model, how many dollars was Jane’s initial deposit? (Disregard the $ sign when gridding your answer.)
The amount, a, that Jane has deposited after t fixed weekly deposits is equal to the initial deposit plus the total amount of money Jane has deposited in the t fixed weekly deposits. This amount a is given to be . The amount she deposited in the t fixed weekly deposits is the amount of the weekly deposit times t; hence, this amount must be given by the term in (and so Jane must have deposited 18 dollars each week after the initial deposit). Therefore, the amount of Jane’s original deposit, in dollars, is