Consider the following page reference string: 1, 2, 1, 3, 2, 4, 2, 1, 5, 6, 2, 1, 2, 3, 7, 6, 3, 2, 1, 2, 3, 7, 6 How many page faults would occur for the following replacement algorithms assuming four, or seven frames? Remember that all frames are initially empty, so your first unique pages will all cost one fault each. (a) LRU replacement (b) FIFO replacement (c) optimal replacement Show your steps and tabulate your results in the following format