Initial amount= $5080.
Interes rate=21%
The final quatity is given by:
![PMT=(PV*i)/(1-(1+i)^(-n))](https://img.qammunity.org/2023/formulas/mathematics/college/pzivsbjojxvy45no5lmre0li26xdhf6cgn.png)
Where,
PV= initial amount= $5080
i=rate of interest =21%
n= time in years =3 years
Replacing:
![\begin{gathered} A=(5080*0.21)/(1-(1+0.21)^(-3)) \\ A=279.66 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/ut7ioby08quzo0llcgqecluiyhuc8lu17z.png)
He has to pay $279.66 each month.
B) Total interest.
Final amount-initial amount:
![\begin{gathered} TotalInterest=279.66*(12*3)-5080= \\ =4987.76 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/ahx3crex60y5ajeb6kjfokltl1fsbbyo55.png)
The total interest he had to pay is: $4987.76.