Installment Sales Method

[omaruko]

Hi all

Pls. help me out how to solve the following problem

Pie Co. uses the installment sales method to recognize revenue,
Customers pay the nstallments notes in 24 equally　monthly amounts, which include 12% interest. What is an installment note's receivable balance 6 months after the sale?

Question：The present value of the remaining monthly payments discounted at 12%
or　75％　of　the　original　sales　prices

Answer is: The present value of the remaining monthly payments discounted at 12%

I transact

Note　Receivable　200　Installment　180
　　　　　　　　　　　　　　　D.N.R　　　　20

Receipt 25％　of　proceed
Cash　　　　45　　Note　Receivable　50　
D.N.R　　　　5

Balance is

Note　Receivable　150　Installment　135　　　　
　　　　　　　　　　　　　　　D.N.R　　　　15

I suspect that　 75％　of　the　original　sales　prices is correct answer.