Chapter 4 - Writing Linear Functions - 4.3 - Writing Equations of Parallel and Perpendicular Lines - Exercises - Page 191: 6

None of them are parallel since slopes are different.

Slope of line $a$ $=\frac{y_{2}-y_{1}}{x_{2}-x_{1}}=\frac{9-3}{1-(-1)}=\frac{6}{2}=3$ Slope of line $b$ $=\frac{14-12}{-1-(-2)}=\frac{2}{1}=2$ Slope of line $c$ $=\frac{10-8}{6-3}=\frac{2}{3}$ Slopes are different for lines $a,b$ and $c$. So, none of them are parallel.