Consider a system with memory access time 50nsec and demand paging with the page table held in MMU registers. It takes 4msec to service a page fault if an empty page is available and 8msec if replaced page is modified. a How long it takes to service a page fault if the replaced page is not modified? b. Assuming that the page to be replaced is modified 5% of time, an empty page is available 80% of time and the page to be replaced is not modified 15%, what is the maximum acceptable page fault rate for an effective access time of no more than 60nsec