consider a paging system with the page table stored in memory. (a) if a memory reference takes 50 nanoseconds, how long does a paged memory reference take? (b) if we add tlbs, and if 75 percent of all page-table references are found in the tlbs, what is the effective memory reference time? (assume that finding a page-table entry in the tlb stakes 2 nanoseconds, if the entry is present.)