Solve the point a and b step by step (30 points)

a) A company signs a promissory note for $120,000 at 90 days, at 25%. Thirty days later, he contracts a debt of $100,000 to pay it off 2 months later, without interest. Two months after the first date, you agree with a creditor to pay $150,000 at that time and, to pay off the rest of your debt, make a final payment 3 months after the last date, with 30% interest. Determine the final agreed payment

b) Agro inputs sells agricultural inputs in the central-eastern region of the country, one of the establishments that sells its products requests merchandise for an amount of 25 million pesos to pay them in installments. The company charges a rate of 1.5% per month for installment payments of less than 120 days. The establishment agrees to pay the total of the merchandise in the following way: an initial payment of 20% of the total debt, at 30 and 60 days a value of $1,800,000, at 90 days an amount of $5,000,000 and the remaining value at 120 days. What is the final value paid and the interest generated by the merchandise. Solve by business and American rule