The formula to calculate the monthly payment is given to be:
![A=P\cdot(r(1+r)^n)/((1+r)^n-1)](https://img.qammunity.org/2023/formulas/mathematics/college/6knpi4xxdt7moy55ibxa4dpnljorfwm2bk.png)
where
![\begin{gathered} A=\text{ Monthly Payment} \\ P=\text{ }Loan\text{ amount} \\ r=\text{ }Interest\text{ rate per period} \\ n=\text{ Total number of periods} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/8bedaxsff773ye8sv1zh78r490oagmdx19.png)
From the question provided, we have the following parameters:
![\begin{gathered} P=4,000 \\ r=(0.15)/(12)=0.0125 \\ n=3*12=36\text{ months} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/cjqfrn133960db8jpcn9g8akqw2397sj5j.png)
Therefore, we can input these values into the formula and calculate the monthly payment as follows:
![\begin{gathered} A=4000*(0.0125*(1+0.0125)^(36))/((1+0.0125)^(36)-1) \\ A=138.66 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/f5yrlncenaadbub8rmjswkmogu542ilgyl.png)
The amount to be paid monthly is $138.66