PT ABC is considering a new machine option for their factory, whether the machine made by Xeros inc or Simp inc. The price of PT Xeros machine is quite cheap, which only costs Rp20 billion, but needs maintenance every 6 months, which costs Rp10 billion. Meanwhile, the price of simp inc machine is more expensive, which costs Rp50 billion and needs maintenance every 6 months, which only costs Rp5 billion. a) Which machine is cheaper in terms of cost if the cost of capital of PT ABC is 1X.Y% a year. The machine has an economic life of 8 semesters. b) PT ABC's plan to buy the machine will still be carried out in 3 years. Currently PT ABC has prepared 20 billion. The rest of the money needed will be added every semester. How much PT ABC needs to add in each semester to cover the initial purchase price and the maintenance cost?

Note X=1 Y=1