What is the need to achieve population inversion​

What is the first step in creating a maintenance ?

Acomputer has a two-level cache. suppose that 60% of the memory references hit on the first level cache, 35% hit on the second level, and 5% miss. the access times are 5 nsec, 15 nsec, and 60 nsec, respectively, where the times for the level 2 cache and memory start counting at the moment it is known that they are needed (e.g., a level 2 cache access does not even start until the level 1 cache miss occurs). what is the average access time?

Suppose a cpu with a write-through, write-allocate cache achieves a cpi of 2. what are the read and write bandwidths (measured by bytes per cycle) between ram and the cache? (assume each miss generates a request for one block.)