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F = 7/- 8 + 5/6 - 1
                 4
F = - 7/8 + 5/6 - 1
                  4
F = - 7/8 + 5/6 x 1/4 - 1
F = - 7/8 + 5/24 - 1
F = - 7 x 3 / 8 x 3 + 5/24 - 1 x 24 / 1 x 24
F = - 21/24 + 5/24 - 24/24
F = - 20/24
F = 4 x - 5 / 4 x 6
F = - 5/6