how to write (6,8) and M=1/2 in slope intercept form?

The slope Intercept form is : 

$Y = mx + b$

where m is the slope of the line 

b is the point of intersection with the Y axis . 

for the point ( 6,8) and m = 1/2 

$8 = \frac{1}{2}*6 + b$

$8 = 3 + b$

$b = 8 - 3$

$b = 5$

 $Y = \frac{1}{2}x + 5$