A straight line, $$\(l\)$$, has equation $$\(y=5 x+12\)$$. A line perpendicular to line $$\(l\)$$ has gradient $$\(k\)$$. Find the value of $$\(k\)$$. $$\[ k=....................... \]$$

E3.6 Find the gradient of parallel and perpendicular lines. (e.g. find the gradient of a line perpendicular to y = 3x + 1.) (e.g. find the equation of a line perpendicular to one passing through the coordinates(1, 3) and (–2, –9).)