Please explain the intermediate steps using formulas.

NOT with EXCEL and not just an explanation without the steps

I need to underatand it to study it and I am making a mistake somewhere

Thank you!

Exercise 5 (10 Points) Each month (by the beginning of the month) for a period of 5 years Inna saves 100 in a savings account. After the five years she increases the amount to 600 per month and saves for an additional 5 years. After 10 years she buys a condo for 120,000. The interest rate of the savings account is 0.5% per annum and the interest rate for the credit is 1% per annum. a) (6 Points) How much has she saved up by the end of the 10 years? b) (4 Points) The remainder of the costs she plans to pay back over a period of 10 years. This she wants to realize with constant rates paid on the first of each month. What is the annuity she has to pay each month? Solution: a) K10=42691.5991 b) Remainder =77308.4009a=676.6895