Assuming that the account earns the interest as simple interest, to calculate the amount Mrs. Martin will have after 18 months, you have to use the following formula:
Where
A is the accrued amount
P is the principal amount
r is the interest rate expressed as a decimal number
t is the time expressed as years
She deposited $2300, this is the principal amount.
The interest rate of the account is 1.5%, to express it as a decimal value you have to divide it by 100
To express the time in "years" you have to divide the given months by 12
Now that all values are expressed in their corresponding units, you can calculate the final balance in her account as:
After 18 months she will have $2351.75 in her account.