Glencoe Algebra 2, Chapter 2, 2.4, Section 2.4, Problem 36

Given an equation of a line L1 is y = 1/4 x + 7
y = 1/4 x + 7

so the slope of the line L1 be m_1 is = 1/4
as we know that the product of the slopes of the two perpendicular lines is equal to -1
let the slope of the required line is m_2
so ,
(m_1)(m_2) = -1
=> m_2 = -4
As,the slope-intercept form of the required line is
y= (m_2)x+b
from the above we know m_2 = -4 , so the line equation is
y= (-4)x+b --------------(1)
we need to find the value of b , as the line passes through the point
(x,y)= (2, -5 ) , then on substituting we get
-5 =(-4)*(2)+b
=> b = -5 +8 = 3
so the equation of the line is
y= (-4)x+ 3