7. (15 pts) Considering a paging-based VAS (Virtual Address Space), assume that addresses are 64-bit and pages occupy 1KB (210 bytes). In addition, entries in any level of a page table spans 4 bytes. a. (4 pts) If the implementation maintains a linear page table (single level), how many bits are used for representing VPNs (Virtual Page Numbers)? b. (6 pts) Again, if the implementation maintains a linear page table, how many pages does this page table use? C. (5 pts) If the implementation maintains a page directory (2-level page table) to keep track of page table pages, how many bits are needed for representing page directory indices