Use the completed X diagram to replace the x-term in the trinomial with two x-terms.
x2 + x – 42 = x2 +– 42
Next, use double grouping to factor the four terms.
= x()–(x + 7)
=
To verify, the factors.

answer:  

\boxed {\frac{1}{5}}  

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solution-

60 *   \frac{1}{5}   = 12

90 * \frac{1}{5} = 18

75 * \frac{1}{5} = 15

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hence, the answer would be \boxed {\frac{1}{5}}