12x is your answer.
c. y = 1/4 x + 5
first, put the equation of the line on the graph into slope-intercept form
(y = mx + b): y = -4x + 8
second, a perpendicular line has to have "an opposite/reciprocal slope" to the original slope. so, find the "m" value in your original equation (it's -4, right? )
original slope: m = -4 perpendicular slope: change the sign to its opposite and find the reciprocal ("flip" the number)
new slope is now positive (b/c the original slope was negative 4), and it's 1/4 (not the original slope of 4 or 4/1)
you can use a^2+ b^2=c^2