Question 150781
First find the slope of the line that passes through those two points. 
The formula for slope is,
{{{m=(y[2]-y[1])/(x[2]-x[1])}}}
{{{m=(3-7)/(9-4)}}}
{{{m=-(4/5)}}}
Perpendicular lines have slopes that are negative reciprocals of each other.
{{{m[1]m[2]=-1}}}
{{{-(4/5)m[2]=-1}}}
{{{m[2]=5/4}}}
D) 5/4