Question 313263
First find the slope of the known equation:

{{{x + 7y = 70}}}

change the equation to slope-intercept form.

solve for y, subtract x from both sides {{{7y = -x + 70}}}

Divide both sides by 7------------------{{{7y/7=(-x/7) + (70/7)}}}

Simplify into slope-intercept form------{{{y = (-1/7)x + 10}}}

So the slope is -1/7. The slope of the perpendiculoar line must be the inverse reciprocal of the original. {{{-1/7}}} becomes {{{7/1 = 7}}} 

Now solve the second equation for y. ---- {{{y = kx -3}}}

replace k with the new slope--------------{{{y=7x-3}}}, so k = 7