I think the price of the car 2995 is too low for a down payment as high as 2138, so for now I’ll use P to represent the price of the car, then substitute for P later.
Amount left to pay (amount borrowed)=P-2138. The monthly repayment formula should be:
rp/(1-(1/(1+r)^t)) as you have indicated. So p=P-2138, t=60, r=(11/12)/100=11/1200 per month.
Therefore monthly repayment=0.021742(P-2138).
Now we can substitute values for P.
P=2995: 18.63 a month
P=29995: 605.68 a month
P=21995: 431.74 a month
P=21380: 418.37 a month (that is, 10% down payment)