Spcitic SPane.exet./(leaine )(FaS fer sa ' e D. A computer has a cache, a main memory, and a disk used for virtual memory. If a word is in the cache, 20 ns are required to access it. If it is in the main memory. but not in the cache, 60ns are required to load it into the cache, and then the reference is started again. If the word is not in main memory, TU'ms are required to copy it to the eache, and then the reference is started again. The eache hit ratio is 0.9 fetch the word from disk, followed by 60 ns to main memory hit ratio is 0.99, what is the average time in ns to access a word on this system IMark)