18. A couple is opening a savings account for a newborn baby. They start with $\mathrm{\$}3,450$ received in baby gifts. If no deposits or withdrawals are made, what is the balance of the account if it earns simple interest at $5\mathrm{\%}$ for 18 years?

Step 1 ：The problem is asking for the balance of a savings account after 18 years with a starting balance of $3450 and an annual interest rate of 5%. This is a simple interest problem, so we can use the formula for simple interest to solve it.

Step 2 ：The formula for simple interest is: $$A=P(1+rt)$$ where: $$A$$ is the amount of money accumulated after n years, including interest, $$P$$ is the principal amount (the initial amount of money), $$r$$ is the annual interest rate (in decimal), and $$t$$ is the time the money is invested for, in years.

Step 3 ：In this case, $$P=3450$$, $$r=5\mathrm{\%}=0.05$$, and $$t=18$$ years. We can substitute these values into the formula to find the final balance of the account.

Step 4 ：Substituting the values into the formula, we get: $$A=3450(1+0.05\times 18)$$

Step 5 ：Solving the equation, we find that $$A=6555.0$$

Step 6 ：Final Answer: The balance of the account after 18 years will be $\boxed{{\displaystyle 6555}}$