Consider the following page-reference string in virtual memory management: 1, 2, 8, 3, 4, 2, 1, 5, 6, 2, 1, 3, 7, 6, 3. Assuming four frames, how many page faults would occur for the following replacement algorithms? Remember that all frames are initially empty, so all of your first unique pages will cost one fault each. 3. (a) LRU replacement (b) FIFO replacement (c) Optimal replacement