A computer has a cache, main memory, and a disk used for virtual memory. If a referenced word is in the cache, 20 ns are required to access it. If it is in main memory, but not in the cache, 60 ns are needed to load it into the cache (this includes the time to originally check the cache), and then the references is started again. If the word is not in main memory, 12 ms are required to fetch the word from disk, followed by 60 ns to copy it to the cache, and then the reference is started again. The cache hit ratio is 0.9 and the main-memory hit ratio is 0.6. What is the average time in ns required to access a referenced word on this system? Show your work for this problem. Please discuss or explain the steps you used to get to your final answer (e.g. if you just give me the final average access time and it is wrong, you will not receive any points). For your reference, 1 ms (millisecond) = 1,000,000 ns (nanoseconds)