well, do a payments table of values, just like before for each mont hmm let's see
1st month.......................3500 + p(1)
2nd month....................3500 + p(2)
3rd month.....................3500 + p(3)
4th month.....................3500 + p(4)
5th month.....................3500 + p(5)
36th month..................3500 + p(36)
![\bf \stackrel{\textit{total value}}{17900}=\stackrel{\textit{down payment}}{3500}+\stackrel{\stackrel{\textit{payments for}}{\textit{36 months}}}{36p} \\\\\\ 14400=36p\implies \cfrac{14400}{36}=p\implies 400=p](https://img.qammunity.org/2020/formulas/mathematics/middle-school/khkljheu444g6epz82z24w6ljzj36tm83e.png)