A computer has a cache, main memory, and a disk used for virtual memory. If a referenced word is in the cache, $30$ ns are required to access it$,$ and transfer the data back to the CPU. If it is in main memory but not in the cache, $80$ ns are needed to access it and load it into the cache. If the word is not in main memory, $36$ ms are required to fetch the word from disk, loading into main memory. The cache hit ratio is $0\mathrm{.}7$ and the main memory hit ratio is $0\mathrm{.}9.$ What is the average time required to access a referenced word on this system?