Glencoe Algebra 2, Chapter 2, 2.3, Section 2.3, Problem 45

The line which we needed is perpendicular to y= 3 .
the product of the slopes of two lines which are perpendicular is equal to -1
let the slope of the line which we need to find be m_1 and the slope of the line y= 3 be m_2 .
so ,
m_1 * m_2 = -1
as the slope of the line y=3 is m_2 = 0 ,
so , slope of m_1 is
m_1 * (0) = -1
=> m_1 = -1/0 = oo= undefined
so this is a vertical line to be plotted on the graph , as this line passes through (3,3) so the graph is as follows