Chapter 6 - Section 6.1 - Rational Expressions and Functions; Multiplying and Dividing - Exercise Set - Page 414: 34

$\frac{6}{y+7}$ (and $y\ne7$).

The product of a binomial sum and a binomial difference is: $(A+B)(A-B)=A^2-B^2$. Hence here: $\frac{6y-42}{y^2-49}=\frac{6(y-7)}{y^2-7^2}=\frac{6(y-7)}{(y+7)(y-7)}=\frac{6}{y+7}$ (and $y\ne7$).