write the general equation form of the line 
which passes through the 2 points: (1,2), (6,7)

You need two formulas:

     y2 - y1
m = --------- to find the slope, m, and
     x2 - x1

then you substitute the value you get for m, then 
substitute the values for x1 and y1. Do not
substitute anything for x and y.  Just leave them
variable:

y - y1 = m(x - x1)

(x1,y1) = (1,2), (x2, y2) = (6,7)

so

     y2 - y1     7 - 2     5
m = --------- = ------- = --- = 1
     x2 - x1     6 - 1     5

Then 

y - y1 = m(x - x1) becomes

 y - 2 = 1(x - 1)

 y - 2 = x - 1
   + 2     + 2
 -------------
 y     = x + 1

That's the equation:

     y = x + 1

Edwin