If I want to purchase a vehicle with an OTR $($On$-$The$-$Road$)$ price of IDR $468,733,000,$ the

following is known: for a $36-$month installment plan, the down payment $($DP$)$ is IDR $84,406,000$

with a monthly installment of IDR $14,603,000.$ For a $48-$month installment plan, the DP is IDR

$84,406,000$ with a monthly installment of IDR $11,960,000.$ For a $60-$month installment plan, the

DP remains the same at IDR $84,406,000$ with a monthly installment of IDR $10,317,000.$ Determine:

a$.$ The best installment payment scheme for the buyer

b$.$ The best installment payment scheme for the seller