consider the following page reference string: 1, 2, 3, 4, 1, 3, 5, 6, 3, 2, 7, 1, 2, 1, 7, 6, 5, 3, 2, 1 remember that all frames are initially empty, so your first unique pages will cost one fault each. how many page faults would occur for the following replacement algorithms, for fifo with four frames? (show work)