Answer:
n= -4
Step-by-step explanation:
First we have to find the equation of line which passes through (6,3) and (8,4).
Then we have to pass this line through the point (n , -2).
we know, equation of line passing through (x1,y1) and (x2,y2) is

So, the equation of line passing through (6,3) and (8,4) is

or, 
multiplying both sides by -2
x-6=2(y-3)
or, x-6=2y-6
or, x-2y=6-6
or, x-2y=0
Now, we have to pass this line through (n,-2)
So, using the point in the line, that is using x=n , y=-2
we get
n-2(-2)=0
or, n+4=0
or, n=-4