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Factor each trinomial mentally
    x^2 -8x + 7 = (x-1)*(x-7)
    x^2 -6x - 7 = (x-7)*(x+1)
    x^2 +7x + 6 = (x+1)*(x+6)
    x^2 -x - 42 = (x-7)*(x+6)
Then write your expression as the product of fractions and make all necessary reductions.
As simple as 2 x 2 = 4.
Solved  (i.e. fully explained)