In the following exercises, decide whether it would be more convenient to solve the system of equations by substitution or elimination.
(6) $\left\{\begin{array}{l}14 x-15 y=-30 \\ 7 x+2 y=10\end{array}\right.$
(6) $\left\{\begin{array}{l}x=9 y-11 \\ 2 x-7 y=-27\end{array}\right.$