$$Nadia bought a bedroom set at RM$2,727$ cash by installment. She was charged an interest of $15\%$ based on the reducing balance. She has to pay a down payment of RM$666$ and equal payments for $2$ years. Find; 

 

i$.$ the monthly payment using the Constant Ratio Formula,

ii$.$ the installment price,

iii. the amount of the outstanding balance just after the $18$th payment using Rule of $78.$