Explanation:
the slope of a line is the ratio
y coordinate difference / x coordinate difference
when going from one point on the line to another.
so, when going from (3, 7) to (10, 10) :
x changes by +7 (from 3 to 10).
y changes by +3 (from 7 to 10).
therefore, the slope is +3/+7 = 3/7