A person saves money every month in such a way that the amounts saved form an arithmetic progression. The amount saved in the 10th month is ₹2,500, and the total amount saved in the first 12 months is ₹25,800.
a. (i) Find the amount saved in the first month and the monthly increase in savings.
b. (ii) Using these values, determine the total amount the person will have saved in 18 months.