find the slope between the points A(a+b,4m-n) and B(a-b,m+2n)

(a + b, 4m - n)   = ( X2, Y2)

(a -  b, m + 2n)    =  (X1, Y1)

So.....the slope is

[ (4m -  n) - (m + 2n)]

__________________      simplify

[ (a + b) - (a - b) ]

[ 3m -3n ]

________ 

   2b

3 [ m - n]

_______

   2 b

find the slope between the points A(a+b,4m-n) and B(a-b,m+2n)