Suppose that the processor has access to three levels of cache memory. Level 1 has an access time of 0.015 s; Level 2 has an access time of 0.15 us; Level 3 has an access time of 0.25 s; Suppose 80% of the memory accesses are found in level 1, 15% of the memory accesses are found in level 2, 5% of the memory accesses are found in level 3. Then what is the average access time to words ?