Question 918979
the standard slope-intercept form for an equation of a line is 
{{{y = highlight_green(m)x + highlight(b)}}}  where m is the slope and b the y-intercept.  
5x-7y=39 Solving for y
y = {{{ highlight_green(5/7)}}}x - 39/7, m = (5/7)

the slope of a line perpendicular: m = -7/5 (negative reciprocal) {{{(5/7)(-7/5) = -1}}}