[tex]\text{First, we have to find the slope of line a}\\\\\text{Use the slope formula:}\\\\\frac{y2-y1}{x2-x1}\\\\\frac{10-14}{9-4}\\\\\text{Solve:}\\\\\frac{10-14}{9-4}\\\\\frac{-4}{5}\\\\\text{Since we know parallel lines have the same slope, the slope of line be is}\\\frac{-4}{5}\\\\\boxed{\frac{-4}{5}}}[/tex]
