[tex]\text{Let}\\\\k:y=m_1x+b_1\\\\l:y=m_2x+b_2\\\\l\ \perp\ k\iff m_1m_2=-1\to m_2=-\dfrac{1}{m_1}\\\\l\ \parallel\ k\iff m_1=m_2\\\\===================================\\\\\text{We have the equation of a line:}\ y=-\dfrac{2}{5}x+\dfrac{4}{5}\to m_1=-\dfrac{2}{5}.\\\\m_2=-\dfrac{1}{m_1}\to m_2=-\dfrac{1}{-\frac{2}{5}}=\dfrac{5}{2}[/tex]
