A company buys a machine for Rs 3,00,000. Its value depreciates by 20\% at the end of every year. Treat the successive yearly depreciations as forming a geometric progression. Answer the following:
a. (i) Calculate the total amount by which the machine depreciates in the first five years.
b. (ii) Find the least number of complete years after which the total depreciation will exceed 90\% of the original cost.