Question 163923
6 over r + 9 over r-7 
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(6/r) + (9/(r-7))

lcd: r(r-7)

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Rewrite each fractionwith the lcd as its denominator:

(6(r-7))/lcd + (9r)/lcd

Combine the numerators over the lcd:

[6r-42+9r]/lcd

Simplify:

= (15r - 42)/(r(r-7))

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Cheers,
Stan H.