Given:
The principal amount is P = $3000.
The rate of interest is r = 5% = 0.05.
The interest rate is A = $600.
The objective is,
a) To find the number of years.
b) To find the monthly payment.
Step-by-step explanation:
a)
The general formula for simple interest is,

To find n:
On plugging the given values in equation (1),

b)
Since, the total amount of the item can be calculated as,

On plugging the obtained values in equation (2),

To find monthly payment:
Now, the monthly payment can be calculated as,

Here, m represents the monthly payment, the product of 12 is used to convert the number of years into the number of months.
On plugging the obtained values in equation (3),

Hence,
a) The number of years is 4 years.
b) The monthly payment is $75.