6. A system has a main memory with a cache plus a disk for virtual memory. The cache access time is 20nsec and the hit ratio for the cache is 90%. If the data being referenced is not in the cache, then it must first be loaded to the cache and then read from the cache into the processor. The load from main memory to the cache takes 60 nsec. If the data is not in main memory then it must first be fetched from the disk which takes 12 msec followed by 60 nsec to copy it to the cache from main memory. If the main memory hit ratio is just 60% what is the average access time for this system? Show all work