Given is the equation that models the amount deposited by Jane $ a = 18t + 15 $ .
Jane made an initial deposit to a saving to the 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 $ t $ weekly deposits. According to the model, how many dollars was Jane’s initial deposit? \[(Disregard{\text{ }}the\;sign{\text{ }}when{\text{ }}gridding{\text{ }}your{\text{ }}answer.)\]

Hint: These types of problems are complicated to see but these types of problems are easy. When an equation is written in terms of time $ t $ and initial value is asked then we just put $ t = 0 $ and start solving these equations.

Complete step-by-step answer:
The given equation of deposited amount by Jane is
Deposited amount $ (a) = 18t + 15 $ …. (1)
To calculate the initial deposited amount by putting $ t = 0 $
Deposited amount $ (a) = 18 \times 0 + 15 $
Deposited amount $ \left( a \right) = 15 $
The dollar sign is disregarded due to given in question
So our initial deposited amount is $ 15 $ .

Note: There may be a given polynomial equation of any quantity which changes with time $ t $ then the process of solving these type problems will be the same. Avoid any type of calculation mistake while solving polynomial equations.