You have the points (2,10) and (10,1). In order to find the slope in between these points, use the following formula:
m = (y2 - y1)/(x2 - x1)
where (x1,y1) and (x2,y2) are the given points. Replace the values of the parameters in the previous formula:
m = (1 - 10)/(10 - 2)
m = -9/8 = -1.125
Hence, the slope in between the lines is -1.125